MCore will not load. (CB 1.6.4-R2.0)(Factions 2.2.2)(MCore 6.9.1)(JAVA 7)

[finnthehuman11]

Here is my ERROR message:

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21:51:44 [INFO] This server is running CraftBukkit version git-Bukkit-1.6.4-R2.0-b2918jnks (MC: 1.6.4) (Implementing API version 1.6.4-R2.0)
21:51:44 [SEVERE] Could not load 'plugins/mcore.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: com/massivecraft/mcore/MCore : Unsupported major.minor version 51.0
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:184)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:305)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:230)
at org.bukkit.craftbukkit.v1_6_R3.CraftServer.loadPlugins(CraftServer.java:241)
at org.bukkit.craftbukkit.v1_6_R3.CraftServer.(CraftServer.java:219)
at net.minecraft.server.v1_6_R3.PlayerList.(PlayerList.java:56)
at net.minecraft.server.v1_6_R3.DedicatedPlayerList.(SourceFile:11)
at net.minecraft.server.v1_6_R3.DedicatedServer.init(DedicatedServer.java:107)
at net.minecraft.server.v1_6_R3.MinecraftServer.run(MinecraftServer.java:393)
at net.minecraft.server.v1_6_R3.ThreadServerApplication.run(SourceFile:583)
Caused by: java.lang.UnsupportedClassVersionError: com/massivecraft/mcore/MCore : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:637)
at java.lang.ClassLoader.defineClass(ClassLoader.java:621)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader.java:80)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:53)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173)
... 9 more

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I noticed that this issue is posted quite frequently, and that it often turns out that the user was not using the latest version of Java. I have confirmed multiple times that I do in fact have Java 7. Is there a different issue that can be identified that causes the failure of this plugin to load?

Screenshots:

Thank you for your time!

[oloflarsson]

This issue only happens on Mac. Something is wrong with that OS. Whatever version of Java 7 you are using it's not supporting Java 7 versions.