Power Lock -- Not working perfectly.

In my 96 Camry, I am getting a new problem. One of my rear door lock is NOT released when the central lock switch is pressed. This works sometimes and sometimes this is not. I have marked that when the vehicle is hot this is not working.e.g. After a long day parking in sun. But in the morning this is working great. Any clue?

Thanks,
PK

The linkage is probably gummed-up.Take the inner door panel off and spray the connections with penetrating oil then white grease.

I am not really sure if this is due to any linkage problem or any mechanical problem. Now the lock is not opening at all. Of course when the switch pressed, the lock is trying to open, but could not do so. I was trying to get the door panel out, but I couldn't do so. Any idea how to get the door panel out. I found two big screw ( both are at the handle) and some small srews ( plastic ) around the panel. I have opened all, but still I could not open the door panel. Can anybody advise me how to open the door panel? Any diagram is of help.

Thanks,
PK