There arenumber of things which could cause this problem.
As only one door is remaining locked, the control unit and associated wiring in the fusebox is unlikely to be faulty. This leaves the door motor or the wiring.
As the door locks but doesn't unlock I suspect the motor itself and the wiring to be OK (its a two wire system, put the voltage one way round on the motor, the door will lock, put it the other way round it will unlock).
Try locking yourself in the car, then turning on the ignition and seeing if the check panel shows the passenger door open. This means that the door open microswitch (which has an effect on driving the motor) is faulty or is poorly positioned.
Otherwise the only other possibility (and I think this is unlikely) is that there is another switch in the door lock that sends a command to the control unit to open the rest of the doors. This may be sticky. Try locking the car then opneing the passenger door with the key- do the other doors open? If so try locking the doors the same way. If that works OK then the problem is elsewhere.
Let me know how you get on.