please help?

I have a v reg 2000 1.8 ghia Ford Focas and my central locking packed up yesterday i have replaced the fob battery which is a 3 button fob, and tried resetting the central locking it resets as its supposed to but the key fob is not operating at all, i can lock the car on the passengers side with the key but using the key from the drivers side it locks then automatically re-opens please can you help.