cenral locking

Help! I have a 96 P38 Diesel, originally it had a battery drain problem, which a new battery solved ,for a while,then the problem surfaced again but this time with a twist, the central locking only works off the fob on the rear doors,and the alarm mobilizes. The n/s/f door don,t work at all off key or fob.
When the key is used it locks/unlocks all except n/s/f ?
I have checked wiring and connections in the two front doors, all seam ok, and have tried re-setting the entry code with no change.Is it possible the battery drain issue is connected to central locking problem?
Anybody any ideas or solutions, any advice would be greatly apreciated.

We've just had our door problem sorted See : Locked out my rangie - it could be a similar sensor problem . Also, we have always have an ongoing battery drain problem even . Apparently there is a known RF interference problem with our models (n reg p38)which causes this drain. If you have a good look back through the posts its mentioned -

Good luck
Karen