Some time past, I had all doors working perfectly. Suddenly, nothing worked but the main passenger door. I tried choosing other keyboard keys as the "select exit" assignment with no success, following all the recommendations on this, as well as other forums.
I overlooked the obvious, and judging from the number of posts regarding this issue, I'll bet somebody else did too. By some unknown means, the number "2" (Top keys, not the pad)was reassigned to the "starter 2 on/off" function. It should have been, and I reassigned it back to the "Select Item 2" FS2002 assignment. Everything worked perfectly with all cargo doors opening, including the front end. I am sure this procedure is the same for the numbers 1, 3, and 4 relative to doors, and possibly other functions as well.
Any other key can be assigned to the "select exit" function. I am useing "D". Pressing D, releasing it, then immediately pressing the "2" key works like a charm. (With PSS Panels).
Just be sure the numerical keys in question are assigned to the "select item" functions in the FS2002 assignments. This absence was what led me astray for quite some time.
Hope this helps somebody!