odd power lock problem

I have a 1991 Chevy Caprice Classic LTZ with an odd power door lock problem... The drivers door power lock will lock with the power lock switch, but won't unlock. What on Earth could be the problem???? The car has an aftermarket alarm installed, and the door won't unlock with that either. The only way to unlock the door is with the key, or manually unlock it from inside the vehicle.

maybe its the contacts on the inside of the switch. i sprayed some kind of electrical conductor lubricant into mine and kept fiddling with them till the corrosion wore off. Mine is an 83 and the switches just popped right out so i dont know if yours is the same. But if you do, then be careful, i almost broke mine taking them out.

Remove the latch plate from inside the door, clean the solenoid mechanism, and pay particular attention to the lock bar (the curved, white link at the upper right) and how it engages the linkages.

http://72.19.213.157/files/PowerDoorLatch.jpg

I'll try that this weekend... I will post another reply to let you know if this works!! Thanks for the info!!