Related to #380 .
Fml log: https://gist.github.com/MrGraphic/7550aca11f6ba7383885
Description: Exception in server tick loop

java.lang.ClassCastException: net.minecraft.world.biome.WorldChunkManager cannot be cast to rtg.world.biome.WorldChunkManagerRTG
at rtg.world.gen.ChunkProviderRTG.(ChunkProviderRTG.java:97)
at rtg.world.WorldTypeRTG.getChunkGenerator(WorldTypeRTG.java:37)
at com.emoniph.witchery.dimension.WorldProviderDreamWorld.func_76555_c(WorldProviderDreamWorld.java:70)
at net.minecraft.world.WorldServer.func_72970_h(WorldServer.java:654)
at net.minecraft.world.World.(World.java:245)
at net.minecraft.world.WorldServer.(WorldServer.java:97)
at net.minecraft.world.WorldServerMulti.(WorldServerMulti.java:14)
at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:65)
at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:92)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:387)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)

Yup , it works now. However Witchery's Dream World lost his important aspect - being overworlds reflection. Well, better this than nothing :).
Thanks

Thanks for reporting.

This should now be fixed in snapshot 3