Sorry to bump this old thread but here's another way to fix this problem if , like me , you're not bothered about the courtesy lights coming on when the faulty door is opened. In my case it was the drivers door causing the problem.
Once you have access to the door lock mechanism you will see the 2 plugs connected to the bottom of it. One with 3 connectors and one with 4. It is the one with 4 connectors that connects to the failing switches. All I did was locate the pair of wires which connect to the courtesy light switches(which were the black & black/white) and cut one of them, thus removing the switch completely out of circuit.
So now the door lock thinks it's closed all the time so no courtesy lights on the drivers door. They still work from all the other doors though. And now my alarm sets properly and I can lock/unlock doors from the switch on the door panel
If you decide to try this don't forget to insulate the wire you cut as there will be 12v on it. I cut it back further in the loom where it was easier to insulate. Also this way it will be easy to re-connect it at a later date if I decide to get a new lock.