Steve, I don't mean to be rude but - my honest advice is: - Delete the prefabs - Follow some tutorials for creating your own basic rooms, buildings, structures - Learn some terrain editing (modsonline / forums here are great) - Get a real feel for building things yourself and how the editor behaves...

I think its because of the general spawns either side, Try making only 1 not sure tho

i got that ERROR too !!!???!?!??!?!?!