Making a tropical-style map and the pools keep freezing over. Only mods I'm using are Optifine Ultra and Worldedit. I try to use //setbiome but it gives me an error message that says "java.lang.NullPointerException: null" Help?
Perhaps you tried changing too large an area and crashed java due to memory limitations? Try doing a very small area and see if it works. If so then scale up until you get a rough idea how large you can go.
Pack Link
You might look into this editor:
http://www.minecraftforum.net/topic/1119044-tool-biome-painter-10-edit-your-minecraft-worlds-biomes/
by c0yote
I tried it with terrible results. I gave my wife my glasses for a second, a creeper showed up and now my wife is pregnant.
Stupid 3D..