2013-07-03 09:14:10 [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_R1.CraftServer.loadPlugins(CraftServer.java:239)
 at org.bukkit.craftbukkit.v1_6_R1.CraftServer.reload(CraftServer.java:603)
 at org.bukkit.Bukkit.reload(Bukkit.java:275)
 at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:23)
 at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:189)
 at org.bukkit.craftbukkit.v1_6_R1.CraftServer.dispatchCommand(CraftServer.java:523)
 at org.bukkit.craftbukkit.v1_6_R1.CraftServer.dispatchServerCommand(CraftServer.java:512)
 at net.minecraft.server.v1_6_R1.DedicatedServer.ar(DedicatedServer.java:262)
 at net.minecraft.server.v1_6_R1.DedicatedServer.t(DedicatedServer.java:227)
 at net.minecraft.server.v1_6_R1.MinecraftServer.s(MinecraftServer.java:487)
 at net.minecraft.server.v1_6_R1.MinecraftServer.run(MinecraftServer.java:420)
 at net.minecraft.server.v1_6_R1.ThreadServerApplication.run(SourceFile:582)
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:631)
 at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
 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:247)
 at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:173)
 ... 14 more