I get this bug with Bukkit 1.6

11:45:49 PM CONSOLE: [WARNING] [Multiverse-Core] Failed to set the generator for world 'world' to 'TerrainControl': java.lang.NoClassDefFoundError: net/minecraft/server/v1_5_R3/WorldProvider
11:45:49 PM CONSOLE: [WARNING] [Multiverse-Core] This is a bug in the generator plugin, NOT a bug in Multiverse!

Yeah, I'm now updating Terrain Control to Minecraft 1.6.1, please be patient.

http://dev.bukkit.org/bukkit-plugins/terrain-control/files/24-terrain-control-v2-4-13/

If it still doesn't work, please leave a message here, and I'll reopen this issue.