I don't know if this is a problem with your underground biomes, with terrain control, or just a general 'both mods can't do this at once' sort of thing. But I've been making tons of custom made biomes with Terrain Control and I wanted to vary the stone found in my world as well so I thought I would try combining the two. Unfortunately the world gets stuck generating.
It would be awesome if there was something you guys could do to make the mod compatible. If not, then I can deal with it, your mod is awesome regardless!