WorldEdit error

2012-03-20 20:41:37 [SEVERE] java.lang.IllegalAccessError: tried to access field net.minecraft.server.TileEntityMobSpawner.mobName from class org.bukkit.craftbukkit.block.CraftCreatureSpawner
2012-03-20 20:41:37 [SEVERE]    at org.bukkit.craftbukkit.block.CraftCreatureSpawner.getCreatureTypeId(CraftCreatureSpawner.java:29)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.bukkit.BukkitWorld.copyFromWorld(BukkitWorld.java:350)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.EditSession.rawGetBlock(EditSession.java:445)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.EditSession.getBlock(EditSession.java:365)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.bukkit.BukkitWorld.regenerate(BukkitWorld.java:213)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.commands.RegionCommands.regenerateChunk(RegionCommands.java:338)
2012-03-20 20:41:37 [SEVERE]    at sun.reflect.GeneratedMethodAccessor157.invoke(Unknown Source)
2012-03-20 20:41:37 [SEVERE]    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
2012-03-20 20:41:37 [SEVERE]    at java.lang.reflect.Method.invoke(Method.java:597)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.minecraft.util.commands.CommandsManager.invokeMethod(CommandsManager.java:514)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.WorldEdit$1.invokeMethod(WorldEdit.java:182)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.WorldEdit$1.invokeMethod(WorldEdit.java:113)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.minecraft.util.commands.CommandsManager.executeMethod(CommandsManager.java:501)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.minecraft.util.commands.CommandsManager.execute(CommandsManager.java:419)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.WorldEdit.handleCommand(WorldEdit.java:1250)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.worldedit.bukkit.WorldEditPlugin.onCommand(WorldEditPlugin.java:197)
2012-03-20 20:41:37 [SEVERE]    at com.sk89q.bukkit.util.DynamicPluginCommand.execute(DynamicPluginCommand.java:40)
2012-03-20 20:41:37 [SEVERE]    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:168)
2012-03-20 20:41:37 [SEVERE]    at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:403)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:791)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:751)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:739)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.Packet3Chat.handle(Packet3Chat.java:33)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.NetworkManager.b(NetworkManager.java:231)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:101)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:78)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:543)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:441)
2012-03-20 20:41:37 [SEVERE]    at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)