How can i fix my central locking on a 1999 peugeot 306, V reg?

Every time I lock my car using the key fob, it takes a second if that before it re-opens.
I can lock all doors from the inside using my drivers knob.
I can unlock all doors but the drivers door using the fob.
I can lock all doors using the drivers key lock.
It used to lock all doors and open all doors via the key fob.
Please help.