WORLDEDIT-3168 - Reported by Atisot.video

mcpc-plus-1.6.4-R2.1-forge965-B256

WE lates forge

22:50:34 [INFO] nik issued server command: /rg define spawn nik
22:50:34 [SEVERE] com.sk89q.minecraft.util.commands.WrappedCommandException: java.lang.ClassCastException: com.sk89q.worldedit.forge.ForgeWorld cannot be cast to com.sk89q.worldedit.bukkit.BukkitWorld
22:50:34 [SEVERE] at com.sk89q.minecraft.util.commands.CommandsManager.invokeMethod(CommandsManager.java:543)
22:50:34 [SEVERE] at com.sk89q.minecraft.util.commands.CommandsManager.executeMethod(CommandsManager.java:520)
22:50:34 [SEVERE] at com.sk89q.minecraft.util.commands.CommandsManager.executeMethod(CommandsManager.java:475)
22:50:34 [SEVERE] at com.sk89q.minecraft.util.commands.CommandsManager.execute(CommandsManager.java:409)
22:50:34 [SEVERE] at com.sk89q.worldguard.bukkit.WorldGuardPlugin.onCommand(WorldGuardPlugin.java:234)
22:50:34 [SEVERE] at com.sk89q.bukkit.util.DynamicPluginCommand.execute(DynamicPluginCommand.java:54)
22:50:34 [SEVERE] at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:192)
22:50:34 [SEVERE] at org.bukkit.craftbukkit.v1_6_R3.CraftServer.dispatchCommand(CraftServer.java:533)
22:50:34 [SEVERE] at net.minecraft.network.NetServerHandler.func_72566_d(NetServerHandler.java:1405)
22:50:34 [SEVERE] at net.minecraft.network.NetServerHandler.chat(NetServerHandler.java:1269)
22:50:34 [SEVERE] at net.minecraft.network.NetServerHandler.func_72481_a(NetServerHandler.java:1201)
22:50:34 [SEVERE] at net.minecraft.network.packet.Packet3Chat.func_73279_a(Packet3Chat.java:68)
22:50:34 [SEVERE] at net.minecraft.network.TcpConnection.func_74428_b(TcpConnection.java:470)
22:50:34 [SEVERE] at net.minecraft.network.NetServerHandler.func_72570_d(NetServerHandler.java:233)
22:50:34 [SEVERE] at net.minecraft.network.NetworkListenThread.func_71747_b(NetworkListenThread.java:54)
22:50:34 [SEVERE] at net.minecraft.server.dedicated.DedicatedServerListenThread.func_71747_b(DedicatedServerListenThread.java:34)
22:50:34 [SEVERE] at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:910)
22:50:34 [SEVERE] at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:330)
22:50:34 [SEVERE] at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:777)
22:50:34 [SEVERE] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:659)
22:50:34 [SEVERE] at net.minecraft.server.ThreadMinecraftServer.run(ThreadMinecraftServer.java:16)
22:50:34 [SEVERE] Caused by: java.lang.ClassCastException: com.sk89q.worldedit.forge.ForgeWorld cannot be cast to com.sk89q.worldedit.bukkit.BukkitWorld
22:50:34 [SEVERE] at com.sk89q.worldedit.bukkit.WorldEditPlugin.getSelection(WorldEditPlugin.java:415)
22:50:34 [SEVERE] at com.sk89q.worldguard.bukkit.commands.RegionCommands.getSelection(RegionCommands.java:252)
22:50:34 [SEVERE] at com.sk89q.worldguard.bukkit.commands.RegionCommands.createRegionFromSelection(RegionCommands.java:275)
22:50:34 [SEVERE] at com.sk89q.worldguard.bukkit.commands.RegionCommands.define(RegionCommands.java:434)
22:50:34 [SEVERE] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
22:50:34 [SEVERE] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
22:50:34 [SEVERE] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
22:50:34 [SEVERE] at java.lang.reflect.Method.invoke(Method.java:606)
22:50:34 [SEVERE] at com.sk89q.minecraft.util.commands.CommandsManager.invokeMethod(CommandsManager.java:533)
22:50:34 [SEVERE] ... 20 more

Comment by Dark_Arc

https://github.com/sk89q/worldedit/blob/master/src/bukkit/java/com/sk89q/worldedit/bukkit/WorldEditPlugin.java#L415