It'* not necessarily a switch thing... it'* more of a fix thing. You should be able to disarm and unlock all doors from either door.
The most likely place for this to fail is right at the key cylinder. The light green wire could have come off. Since it'* such a PITA to take off the door panel, you should test the wire as described above to insure that you aren't going through some unnecessary disassembly.
In this pic, you can see the wire. It'* the light green wire that the T-tap is connected to. It'* mych easier to troubleshoot from here than inside the door.