Toyota Camry Central Locking Problems

[camrsony]

Hi---I would be very grateful if someone would help me with the following problem. I have owned a Toyota Camry 1994 model for over four years and just recently, it has developed major faults with the central locking system. Using the master key I'm able to lock all the doors. However when using the key to unlock, sometimes all four door locks, unlock but on most occasions only the driver door unlocks and hence the other locks have to be opened manually. This is a real nuisance, and I've tried swapping the master door switch located on the door panel with no luck.

When I try to unlock the doors from the master switch on the door panel I can only hear a relay click located in the glove box compartment. Again locking all doors via the master switch isn't a problem.

Could someone please advise me on a possible fault(s).