Hi!!!
Please, make CLEAR topic names: This is help the next user able to find your topic, in the case he has the same qwestion.
Next i'd like to reqwest you use SEARCH more often: This qwestion has been asked millhions of times.
Thank you.
Now to answer your qwestion:
Prefabs are a bit buggy, don't use them.
Just create your room manually, and everything will work fine.
Remember, FPSC is still growing, there are some bugs there, wich are being fixed at the current time.
My love is seperated in 2 parts, 1 of them is 3ds Max 7, the other; FPSC.