WORLDEDIT-2666 - Reported by DerSeegler

14:31:22 [SEVERE] java.lang.UnsupportedClassVersionError: MCPCPlusXNmsBlock_147 : Unsupported major.minor version 51.0
14:31:22 [SEVERE] at java.lang.ClassLoader.defineClass1(Native Method)
14:31:22 [SEVERE] at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
14:31:22 [SEVERE] at java.lang.ClassLoader.defineClass(ClassLoader.java:480)
14:31:22 [SEVERE] at com.sk89q.worldedit.bukkit.BukkitWorld$NmsBlockClassLoader.loadClass(BukkitWorld.java:228)
14:31:22 [SEVERE] at com.sk89q.worldedit.bukkit.BukkitWorld.(BukkitWorld.java:146)
14:31:22 [SEVERE] at com.sk89q.worldedit.bukkit.BukkitUtil.getLocalWorld(BukkitUtil.java:50)
14:31:22 [SEVERE] at com.sk89q.worldedit.bukkit.BukkitPlayer.getWorld(BukkitPlayer.java:132)
14:31:22 [SEVERE] at com.sk89q.worldedit.bukkit.WorldEditListener.onPlayerInteract(WorldEditListener.java:121)
14:31:22 [SEVERE] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
14:31:22 [SEVERE] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
14:31:22 [SEVERE] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
14:31:22 [SEVERE] at java.lang.reflect.Method.invoke(Method.java:616)
14:31:22 [SEVERE] at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
14:31:22 [SEVERE] at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
14:31:22 [SEVERE] at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
14:31:22 [SEVERE] at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
14:31:22 [SEVERE] at org.bukkit.craftbukkit.v1_4_R1.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:178)
14:31:22 [SEVERE] at org.bukkit.craftbukkit.v1_4_R1.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:148)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.PlayerConnection.a(PlayerConnection.java:1019)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.Packet18ArmAnimation.handle(SourceFile:41)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.NetworkManager.b(NetworkManager.java:290)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.PlayerConnection.d(PlayerConnection.java:113)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.ServerConnection.b(SourceFile:39)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.DedicatedServerConnection.b(SourceFile:30)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.MinecraftServer.r(MinecraftServer.java:598)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.DedicatedServer.r(DedicatedServer.java:224)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.MinecraftServer.q(MinecraftServer.java:494)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.MinecraftServer.run(MinecraftServer.java:427)
14:31:22 [SEVERE] at net.minecraft.server.v1_4_R1.ThreadServerApplication.run(SourceFile:849)
14:31:22 [INFO] [WorldEdit] Using inbuilt NmsBlock for this version.

Comment by wizjany

http://youtrack.sk89q.com/issue/WORLDEDIT-2652#comment=67-1680