diff --git a/src/main/kotlin/app/api/Api.kt b/src/main/kotlin/app/api/Api.kt
index 5b58a2e5..a2a5658e 100644
--- a/src/main/kotlin/app/api/Api.kt
+++ b/src/main/kotlin/app/api/Api.kt
@@ -9,11 +9,15 @@ import app.model.Repo
 import app.model.User
 
 interface Api {
-    fun authorize()
-    fun getUser(): User
-    fun getRepo(repoRehash: String): Repo
-    fun postRepo(repo: Repo)
-    fun postCommits(commitsList: List<Commit>)
-    fun deleteCommits(commitsList: List<Commit>)
-    fun postFacts(factsList: List<Fact>)
+    companion object {
+        val OUT_OF_DATE = 1
+    }
+
+    fun authorize(): Result<Unit>
+    fun getUser(): Result<User>
+    fun getRepo(repoRehash: String): Result<Repo>
+    fun postRepo(repo: Repo): Result<Unit>
+    fun postCommits(commitsList: List<Commit>): Result<Unit>
+    fun deleteCommits(commitsList: List<Commit>): Result<Unit>
+    fun postFacts(factsList: List<Fact>): Result<Unit>
 }
diff --git a/src/main/kotlin/app/api/ApiError.kt b/src/main/kotlin/app/api/ApiError.kt
new file mode 100644
index 00000000..981f1d5b
--- /dev/null
+++ b/src/main/kotlin/app/api/ApiError.kt
@@ -0,0 +1,75 @@
+// Copyright 2017 Sourcerer Inc. All Rights Reserved.
+// Author: Anatoly Kislov (anatoly@sourcerer.io)
+
+package app.api
+
+import app.Logger
+import app.model.Error
+import app.model.Errors
+import com.github.kittinunf.fuel.core.FuelError
+import com.google.protobuf.InvalidProtocolBufferException
+import java.nio.charset.Charset
+import java.security.InvalidParameterException
+
+class ApiError(exception: Exception) : Exception(exception.message) {
+    companion object {
+        private val AUTH_ERROR_CODES = listOf(401, 403)
+    }
+
+    // Response content.
+    var httpStatusCode: Int = 0
+    var httpResponseMessage: String = ""
+    var httpBodyMessage: String = ""
+
+    // Server errors from response.
+    var serverErrors = listOf<Error>()
+
+    // Type of errors.
+    var isParseError = false
+    var isAuthError: Boolean = false
+    get() = AUTH_ERROR_CODES.contains(httpStatusCode)
+
+    constructor(fuelError: FuelError) : this(fuelError as Exception) {
+        httpStatusCode = fuelError.response.httpStatusCode
+        httpResponseMessage = fuelError.response.httpResponseMessage
+        if (fuelError.response.httpResponseHeaders["Content-Type"]
+            ?.contains("application/octet-stream") == true) {
+            try {
+                serverErrors = Errors(fuelError.response.data).errors
+            } catch (e: Exception) {
+                Logger.error(e, "Error while parsing errors from server")
+            }
+        } else {
+            httpBodyMessage = fuelError.response.data
+                .toString(Charset.defaultCharset())
+        }
+    }
+
+    constructor(parseException: InvalidProtocolBufferException) :
+            this(parseException as Exception) {
+        isParseError = true
+    }
+
+    constructor(parseException: InvalidParameterException) :
+            this(parseException as Exception) {
+        isParseError = true
+    }
+
+    fun isWithServerCode(serverErrorCode: Int): Boolean {
+        return serverErrors.find { error ->
+            error.code == serverErrorCode } != null
+    }
+}
+
+fun ApiError?.ifNotNullThrow() {
+    if (this != null) {
+        throw this
+    }
+}
+
+fun ApiError?.isWithServerCode(serverErrorCode: Int): Boolean {
+    if (this != null) {
+        return this.isWithServerCode(serverErrorCode)
+    }
+    return false
+}
diff --git a/src/main/kotlin/app/api/MockApi.kt b/src/main/kotlin/app/api/MockApi.kt
index fd4bb8cb..c08688ec 100644
--- a/src/main/kotlin/app/api/MockApi.kt
+++ b/src/main/kotlin/app/api/MockApi.kt
@@ -21,40 +21,45 @@ class MockApi(  // GET requests.
     // DELETE requests.
     var receivedDeletedCommits: MutableList<Commit> = mutableListOf()
 
-    override fun authorize() {
+    override fun authorize(): Result<Unit> {
         Logger.debug { "MockApi: authorize request" }
+        return Result()
     }
 
-    override fun getUser(): User {
+    override fun getUser(): Result<User> {
         Logger.debug { "MockApi: getUser request" }
-        return mockUser
+        return Result(mockUser)
     }
 
-    override fun getRepo(repoRehash: String): Repo {
+    override fun getRepo(repoRehash: String): Result<Repo> {
         Logger.debug { "MockApi: getRepo request" }
-        return mockRepo
+        return Result(mockRepo)
     }
 
-    override fun postRepo(repo: Repo) {
+    override fun postRepo(repo: Repo): Result<Unit> {
         Logger.debug { "MockApi: postRepo request ($repo)" }
         receivedRepos.add(repo)
+        return Result()
     }
 
-    override fun postCommits(commitsList: List<Commit>) {
+    override fun postCommits(commitsList: List<Commit>): Result<Unit> {
         Logger.debug {
             "MockApi: postCommits request (${commitsList.size} commits)"
         }
         receivedAddedCommits.addAll(commitsList)
+        return Result()
     }
 
-    override fun deleteCommits(commitsList: List<Commit>) {
+    override fun deleteCommits(commitsList: List<Commit>): Result<Unit> {
         Logger.debug {
             "MockApi: deleteCommits request (${commitsList.size} commits)" }
         receivedDeletedCommits.addAll(commitsList)
+        return Result()
     }
 
-    override fun postFacts(factsList: List<Fact>) {
+    override fun postFacts(factsList: List<Fact>): Result<Unit> {
         Logger.debug { "MockApi: postStats request (${factsList.size} stats)" }
         receivedFacts.addAll(factsList)
+        return Result()
     }
 }
diff --git a/src/main/kotlin/app/api/Result.kt b/src/main/kotlin/app/api/Result.kt
new file mode 100644
index 00000000..9a56a26a
--- /dev/null
+++ b/src/main/kotlin/app/api/Result.kt
@@ -0,0 +1,19 @@
+// Copyright 2017 Sourcerer Inc. All Rights Reserved.
+// Author: Anatoly Kislov (anatoly@sourcerer.io)
+
+package app.api
+
+data class Result<out T> (val data: T? = null, val error: ApiError? = null) {
+    fun getOrThrow(): T {
+        if (error == null) {
+            return data!!
+        }
+        throw error
+    }
+
+    fun onErrorThrow() {
+        if (error != null) {
+            throw error
+        }
+    }
+}
diff --git a/src/main/kotlin/app/api/ServerApi.kt b/src/main/kotlin/app/api/ServerApi.kt
index 7053d3b3..f475c6a4 100644
--- a/src/main/kotlin/app/api/ServerApi.kt
+++ b/src/main/kotlin/app/api/ServerApi.kt
@@ -12,7 +12,6 @@ import app.model.Fact
 import app.model.FactGroup
 import app.model.Repo
 import app.model.User
-import app.utils.RequestException
 import com.github.kittinunf.fuel.core.FuelManager
 import com.github.kittinunf.fuel.core.Method
 import com.github.kittinunf.fuel.core.Request
@@ -108,22 +107,27 @@ class ServerApi (private val configurator: Configurator) : Api {
 
     private fun <T> makeRequest(request: Request,
                                 requestName: String,
-                                parser: (ByteArray) -> T): T {
+                                parser: (ByteArray) -> T): Result<T> {
+        var error: ApiError? = null
+        var data: T? = null
+
         try {
             Logger.debug { "Request $requestName initialized" }
             val (_, res, result) = request.responseString()
             val (_, e) = result
             if (e == null) {
                 Logger.debug { "Request $requestName success" }
-                return parser(res.data)
+                data = parser(res.data)
             } else {
-                throw RequestException(e)
+                error = ApiError(e)
             }
         } catch (e: InvalidProtocolBufferException) {
-            throw RequestException(e)
+            error = ApiError(e)
         } catch (e: InvalidParameterException) {
-            throw RequestException(e)
+            error = ApiError(e)
         }
+
+        return Result(data, error)
     }
 
     private fun getVersionCodeHeader(): Pair<String, String> {
@@ -134,16 +138,16 @@ class ServerApi (private val configurator: Configurator) : Api {
         return Pair(HEADER_CONTENT_TYPE, HEADER_CONTENT_TYPE_PROTO)
     }
 
-    override fun authorize() {
+    override fun authorize(): Result<Unit> {
         return makeRequest(createRequestGetToken(), "getToken", {})
     }
 
-    override fun getUser(): User {
+    override fun getUser(): Result<User> {
         return makeRequest(createRequestGetUser(), "getUser",
                            { body -> User(body) })
     }
 
-    override fun getRepo(repoRehash: String): Repo {
+    override fun getRepo(repoRehash: String): Result<Repo> {
         if (repoRehash.isBlank()) {
             throw IllegalArgumentException()
         }
@@ -152,25 +156,25 @@ class ServerApi (private val configurator: Configurator) : Api {
                            { body -> Repo(body) })
     }
 
-    override fun postRepo(repo: Repo) {
-        makeRequest(createRequestPostRepo(repo),
-                    "postRepo", {})
+    override fun postRepo(repo: Repo): Result<Unit> {
+        return makeRequest(createRequestPostRepo(repo),
+                           "postRepo", {})
     }
 
-    override fun postCommits(commitsList: List<Commit>) {
+    override fun postCommits(commitsList: List<Commit>): Result<Unit> {
         val commits = CommitGroup(commitsList)
-        makeRequest(createRequestPostCommits(commits),
-                    "postCommits", {})
+        return makeRequest(createRequestPostCommits(commits),
+                           "postCommits", {})
     }
 
-    override fun deleteCommits(commitsList: List<Commit>) {
+    override fun deleteCommits(commitsList: List<Commit>): Result<Unit> {
         val commits = CommitGroup(commitsList)
-        makeRequest(createRequestDeleteCommits(commits),
-                    "deleteCommits", {})
+        return makeRequest(createRequestDeleteCommits(commits),
+                           "deleteCommits", {})
     }
 
-    override fun postFacts(factsList: List<Fact>) {
+    override fun postFacts(factsList: List<Fact>): Result<Unit> {
         val facts = FactGroup(factsList)
-        makeRequest(createRequestPostFacts(facts), "postFacts", {})
+        return makeRequest(createRequestPostFacts(facts), "postFacts", {})
     }
 }
diff --git a/src/main/kotlin/app/hashers/CodeLongevity.kt b/src/main/kotlin/app/hashers/CodeLongevity.kt
index bddfe087..e28c7166 100644
--- a/src/main/kotlin/app/hashers/CodeLongevity.kt
+++ b/src/main/kotlin/app/hashers/CodeLongevity.kt
@@ -22,7 +22,6 @@ import org.eclipse.jgit.revwalk.RevWalk
 import org.eclipse.jgit.treewalk.TreeWalk
 import org.eclipse.jgit.util.io.DisabledOutputStream
 
-import java.io.InputStream
 import java.io.File
 import java.io.FileInputStream
 import java.io.FileNotFoundException
@@ -211,7 +210,7 @@ class CodeLongevity(private val serverRepo: Repo,
         }
 
         if (stats.size > 0) {
-            api.postFacts(stats)
+            api.postFacts(stats).onErrorThrow()
             Logger.info { "Sent ${stats.size} facts to server" }
         }
     }
diff --git a/src/main/kotlin/app/hashers/CommitHasher.kt b/src/main/kotlin/app/hashers/CommitHasher.kt
index dd40535b..aae20917 100644
--- a/src/main/kotlin/app/hashers/CommitHasher.kt
+++ b/src/main/kotlin/app/hashers/CommitHasher.kt
@@ -53,7 +53,10 @@ class CommitHasher(private val serverRepo: Repo = Repo(),
 
                 commit
             }
-            .buffer(20, TimeUnit.SECONDS)  // Group ready commits by time.
+            // Group ready commits by time and count. Max payload 10 mb,
+            // one commit with stats takes around 1 kb, so pack by max 1000
+            // with 10x margin of safety.
+            .buffer(20, TimeUnit.SECONDS, 1000)
             .subscribe({ commitsBundle ->  // OnNext.
                 postCommitsToServer(commitsBundle)  // Send ready commits.
             }, onError)
@@ -70,14 +73,14 @@ class CommitHasher(private val serverRepo: Repo = Repo(),
 
     private fun postCommitsToServer(commits: List<Commit>) {
         if (commits.isNotEmpty()) {
-            api.postCommits(commits)
+            api.postCommits(commits).onErrorThrow()
             Logger.info { "Sent ${commits.size} added commits to server" }
         }
     }
 
     private fun deleteCommitsOnServer(commits: List<Commit>) {
         if (commits.isNotEmpty()) {
-            api.deleteCommits(commits)
+            api.deleteCommits(commits).onErrorThrow()
             Logger.info { "Sent ${commits.size} deleted commits to server" }
         }
     }
diff --git a/src/main/kotlin/app/hashers/FactHasher.kt b/src/main/kotlin/app/hashers/FactHasher.kt
index 4d9a3c58..41332ac0 100644
--- a/src/main/kotlin/app/hashers/FactHasher.kt
+++ b/src/main/kotlin/app/hashers/FactHasher.kt
@@ -82,7 +82,7 @@ class FactHasher(private val serverRepo: Repo = Repo(),
         fsRepoDateStart[email] = timestamp
 
         // RepoDateEnd.
-        if ((fsRepoDateEnd[email] ?: -1) == -1L) {
+        if (fsRepoDateEnd[email]!! == -1L) {
             fsRepoDateEnd[email] = timestamp
         }
 
@@ -137,7 +137,7 @@ class FactHasher(private val serverRepo: Repo = Repo(),
 
     private fun postFactsToServer(facts: List<Fact>) {
         if (facts.isNotEmpty()) {
-            api.postFacts(facts)
+            api.postFacts(facts).onErrorThrow()
             Logger.info { "Sent ${facts.size} facts to server" }
         }
     }
diff --git a/src/main/kotlin/app/hashers/RepoHasher.kt b/src/main/kotlin/app/hashers/RepoHasher.kt
index 7197e297..069a6aa1 100644
--- a/src/main/kotlin/app/hashers/RepoHasher.kt
+++ b/src/main/kotlin/app/hashers/RepoHasher.kt
@@ -88,9 +88,9 @@ class RepoHasher(private val localRepo: LocalRepo, private val api: Api,
                 throw HashingException(errors)
             }
 
-            println("Hashing $localRepo successfully finished.")
+            println("Hashing $localRepo complete finished.")
             Logger.info(Logger.Events.HASHING_REPO_SUCCESS)
-                { "Hashing repo succesfully" }
+                { "Hashing repo completed" }
         }
         finally {
             closeGit(git)
@@ -116,7 +116,7 @@ class RepoHasher(private val localRepo: LocalRepo, private val api: Api,
     }
 
     private fun getRepoFromServer() {
-        val repo = api.getRepo(serverRepo.rehash)
+        val repo = api.getRepo(serverRepo.rehash).getOrThrow()
         serverRepo.commits = repo.commits
         Logger.info{
             "Received repo from server with ${serverRepo.commits.size} commits"
@@ -126,7 +126,7 @@ class RepoHasher(private val localRepo: LocalRepo, private val api: Api,
 
     private fun postRepoToServer() {
         serverRepo.commits = listOf()
-        api.postRepo(serverRepo)
+        api.postRepo(serverRepo).onErrorThrow()
         Logger.debug { serverRepo.toString() }
     }
 
diff --git a/src/main/kotlin/app/model/DiffContent.kt b/src/main/kotlin/app/model/DiffContent.kt
index 82cb7d1e..212eb978 100644
--- a/src/main/kotlin/app/model/DiffContent.kt
+++ b/src/main/kotlin/app/model/DiffContent.kt
@@ -1,3 +1,6 @@
+// Copyright 2017 Sourcerer Inc. All Rights Reserved.
+// Author: Anatoly Kislov (anatoly@sourcerer.io)
+
 package app.model
 
 class DiffContent(
diff --git a/src/main/kotlin/app/model/Error.kt b/src/main/kotlin/app/model/Error.kt
new file mode 100644
index 00000000..0baf8997
--- /dev/null
+++ b/src/main/kotlin/app/model/Error.kt
@@ -0,0 +1,35 @@
+// Copyright 2017 Sourcerer Inc. All Rights Reserved.
+// Author: Anatoly Kislov (anatoly@sourcerer.io)
+
+package app.model
+
+import app.Protos
+import com.google.protobuf.InvalidProtocolBufferException
+import java.security.InvalidParameterException
+
+data class Error(
+    var code: Int = 0,
+    var message: String = ""
+) {
+    @Throws(InvalidParameterException::class)
+    constructor(proto: Protos.Error) : this() {
+        code = proto.code
+        message = proto.message
+    }
+
+    @Throws(InvalidProtocolBufferException::class)
+    constructor(bytes: ByteArray) : this(Protos.Error.parseFrom(bytes))
+
+    constructor(serialized: String) : this(serialized.toByteArray())
+
+    fun getProto(): Protos.Error {
+        return Protos.Error.newBuilder()
+            .setCode(code)
+            .setMessage(message)
+            .build()
+    }
+
+    fun serialize(): ByteArray {
+        return getProto().toByteArray()
+    }
+}
diff --git a/src/main/kotlin/app/model/Errors.kt b/src/main/kotlin/app/model/Errors.kt
new file mode 100644
index 00000000..59b9625a
--- /dev/null
+++ b/src/main/kotlin/app/model/Errors.kt
@@ -0,0 +1,32 @@
+// Copyright 2017 Sourcerer Inc. All Rights Reserved.
+// Author: Anatoly Kislov (anatoly@sourcerer.io)
+
+package app.model
+
+import app.Protos
+import com.google.protobuf.InvalidProtocolBufferException
+import java.security.InvalidParameterException
+
+data class Errors (
+    var errors: List<Error> = listOf()
+) {
+    @Throws(InvalidParameterException::class)
+    constructor(proto: Protos.Errors) : this() {
+        errors = proto.errorsList.map { error -> Error(error) }
+    }
+
+    @Throws(InvalidProtocolBufferException::class)
+    constructor(bytes: ByteArray) : this(Protos.Errors.parseFrom(bytes))
+
+    constructor(serialized: String) : this(serialized.toByteArray())
+
+    fun getProto(): Protos.Errors {
+        return Protos.Errors.newBuilder()
+            .addAllErrors(errors.map { error -> error.getProto() })
+            .build()
+    }
+
+    fun serialize(): ByteArray {
+        return getProto().toByteArray()
+    }
+}
diff --git a/src/main/kotlin/app/model/Fact.kt b/src/main/kotlin/app/model/Fact.kt
index 91daf5a8..e137f1d9 100644
--- a/src/main/kotlin/app/model/Fact.kt
+++ b/src/main/kotlin/app/model/Fact.kt
@@ -1,3 +1,6 @@
+// Copyright 2017 Sourcerer Inc. All Rights Reserved.
+// Author: Anatoly Kislov (anatoly@sourcerer.io)
+
 package app.model
 
 import app.Protos
diff --git a/src/main/kotlin/app/model/FactGroup.kt b/src/main/kotlin/app/model/FactGroup.kt
index 9c00871f..681196d1 100644
--- a/src/main/kotlin/app/model/FactGroup.kt
+++ b/src/main/kotlin/app/model/FactGroup.kt
@@ -1,3 +1,6 @@
+// Copyright 2017 Sourcerer Inc. All Rights Reserved.
+// Author: Anatoly Kislov (anatoly@sourcerer.io)
+
 package app.model
 
 import app.Protos
diff --git a/src/main/kotlin/app/ui/AuthState.kt b/src/main/kotlin/app/ui/AuthState.kt
index 11446e6e..66948e9b 100644
--- a/src/main/kotlin/app/ui/AuthState.kt
+++ b/src/main/kotlin/app/ui/AuthState.kt
@@ -3,13 +3,14 @@
 
 package app.ui
 
-import app.Analytics
 import app.BuildConfig
 import app.Logger
 import app.api.Api
 import app.config.Configurator
 import app.utils.PasswordHelper
-import app.utils.RequestException
+import app.api.ApiError
+import app.api.ifNotNullThrow
+import app.api.isWithServerCode
 
 /**
  * Authorization console UI state.
@@ -20,7 +21,8 @@ class AuthState constructor(private val context: Context,
     : ConsoleState {
     var username = ""
     var password = ""
-    var connectionError = false
+    var retry = true
+    var authorized = false
 
     override fun doAction() {
         if (!configurator.isValidCredentials()) {
@@ -28,13 +30,15 @@ class AuthState constructor(private val context: Context,
             getPassword()
         }
 
-        while (!tryAuth() && !connectionError) {
+        authorized = tryAuth()
+        while (!authorized && retry) {
             getPassword()
+            authorized = tryAuth()
         }
     }
 
     override fun next() {
-        if (!connectionError) {
+        if (authorized) {
             context.changeState(ListRepoState(context, api, configurator))
         } else {
             context.changeState(CloseState())
@@ -68,9 +72,17 @@ class AuthState constructor(private val context: Context,
     fun tryAuth(): Boolean {
         try {
             println("Authenticating...")
-            api.authorize()
+            val (_, error) = api.authorize()
+            if (error.isWithServerCode(Api.OUT_OF_DATE)) {
+                println("App is out of date. Please get new version at " +
+                        "https://sourcerer.io")
+                retry = false
+                return false
+            }
+            // Other request errors should be processed by try/catch.
+            error.ifNotNullThrow()
 
-            val user = api.getUser()
+            val user = api.getUser().getOrThrow()
             configurator.setRepos(user.repos)
 
             println("You are successfully authenticated. Your profile page is "
@@ -81,7 +93,7 @@ class AuthState constructor(private val context: Context,
             Logger.info(Logger.Events.AUTH) { "Auth success" }
 
             return true
-        } catch (e: RequestException) {
+        } catch (e: ApiError) {
             if (e.isAuthError) {
                 if(e.httpBodyMessage.isNotBlank()) {
                     println(e.httpBodyMessage)
@@ -89,10 +101,11 @@ class AuthState constructor(private val context: Context,
                     println("Authentication error. Try again.")
                 }
             } else {
-                connectionError = true
                 println("Connection problems. Try again later.")
+                retry = false
             }
         }
+
         return false
     }
 }
diff --git a/src/main/proto/sourcerer.proto b/src/main/proto/sourcerer.proto
index efa1ca90..f30a9c9a 100644
--- a/src/main/proto/sourcerer.proto
+++ b/src/main/proto/sourcerer.proto
@@ -98,3 +98,13 @@ message Repo {
     // starts after last commit from the overlap.
     repeated Commit commits = 5;
 }
+
+// Errors from server.
+message Error {
+    uint32 code = 1;
+    string message = 2;
+}
+
+message Errors {
+    repeated Error errors = 1;
+}
diff --git a/src/test/kotlin/test/tests/hashers/FactHasherTest.kt b/src/test/kotlin/test/tests/hashers/FactHasherTest.kt
index 33f51e42..f6302188 100644
--- a/src/test/kotlin/test/tests/hashers/FactHasherTest.kt
+++ b/src/test/kotlin/test/tests/hashers/FactHasherTest.kt
@@ -193,7 +193,6 @@ class FactHasherTest : Spek({
                 "2")))
         }
 
-
         afterGroup {
             testRepo.destroy()
         }