Alarm problem , Damp or wiring fault ?

[myfirstrover]

Driving home last night the door open icon popped up in the dash , I got home , checked all the doors , all closed properly , however the alarm wouldn't set and went off continuously when the car was locked , by both the fob and the key , the culprit looks like the rear passenger door , at work today i removed the door card and disconnected the loom to the door lock , this made no difference at all so i unplugged the wiring connector in the B post ,it's all is working ok now , what do we think , damp in the connections or a wiring fault ( 05 plate cdti) ?