Fix for issue #680 + another fix

src/Nancy.Hosting.Aspnet/NancyHandler.cs

@@ -99,14 +99,18 @@ private static void SetNancyResponseToHttpResponse(HttpContextBase context, Resp
             response.Contents.Invoke(context.Response.OutputStream);         
         }
 
+        /// <remarks>
+        /// Copies are made of each collection (Headers, Cookies) for enumeration to avoid
+        /// InvalidOperationExceptions if ASP.NET modifies the response on a different thread.
+        /// </remarks>
         private static void SetHttpResponseHeaders(HttpContextBase context, Response response)
         {
-            foreach (var header in response.Headers)
+            foreach (var header in response.Headers.ToDictionary(x => x.Key, x => x.Value))
             {
                 context.Response.AddHeader(header.Key, header.Value);
             }
 
-            foreach(var cookie in response.Cookies)
+            foreach (var cookie in response.Cookies.ToList())
             {
                 context.Response.AddHeader("Set-Cookie", cookie.ToString());
             }

src/Nancy/Routing/DefaultRouteResolver.cs

@@ -50,7 +50,7 @@ public ResolveResult Resolve(NancyContext context)
 
             if (!string.IsNullOrEmpty(extension))
             {
-                var length = context.Request.Path.Length - (extension.Length + 1);
+                var length = context.Request.Path.Length - extension.Length;
                 context.Request.Url.Path = context.Request.Url.Path.Substring(0, length);
             }