ok think I have isolated the fault now. The car now locks/unlocks fine from the drivers door lock. But will not lock from the armrest switch. I have pulled the armrest switch apart and cannot see any problem with the switch or any dry joints on the PCB. I am assuming there is a fault in the armrest switch circuit board. If someone can point me to a circuit diagram of the switch panel I am sure that I can fix the fault.
Played around with it some more, the locks started randomly operating. The problem goes away when the armrest switch is unplugged