Mr. Umberto: Thanks so much for your reply.
After posting the below reply, I am most pleased to report that a helpful soul in the RC forum was able to supply a solution. It so happens with RC, and not many other add-ons, the situation with number keys conflicting with those of FSX "Number Selection" is handled by RC in that the "Keyboard" is editable. Therefore, I was able to edit RC's number 1 into number 5, number 2 into number 6, etc. Now when I open the cargo doors with x+2, RC no longer responds to the 2 click, as now only a "6" click initiates RC's ATC Clearance request, and a subsequent Pushback request and only a "5" click, instead of a "1" click, initiates a Weather Briefing, and subsequent Contact Ground. Since GSX utilizes mouse clickable responses, instead of key clicks, GSX was never a problem. Mark this solution SOLVED.
Now to my original reply to your reply:
Yes, this was a question regarding the opening of doors and my post was in regard to your non-reply as to the question asked by the original poster, "Which single key?"
Why not use the standard Shift+E+Number, you ask. Well, that combination has been the bane of the sim community for years with numerous posts regarding folks who "just could not get the hang of" getting the time delay right. An answer was to substitute the available "x" in the controls menu to remedy the delay problem experienced by folks. It seemed to reduce the number of folks having problems opening cargo doors, with a simpler x+2.
As for a single key for opening doors, since FSX apparently establishes the "number presses" for door activation, eg. 1=Main, 2=Cargo, 3=Emergency, unless one substitutes a letter for say the "Select Number" 2, that letter would only really substitute for the number 2 and it would open the Cargo doors, but that letter would now also have to be used for "Select Number" 2 and, at the same key press, interfere with RC by requesting an ATC Clearance, while the Cargo doors open. Therefore your earlier suggestion to that poster apparently was misunderstood.
I was under the impression, from your earlier reply to that original poster, that you had a simple answer of "assign a single key to open the cargo doors." I was simply hopeful that your "suggestion" provided a solution and, if not, that some other helpful soul would respond positively, Apparently some add-on providers did not thinkt this numbering sequence through, as they continue to use the numbers 1 through 4, instead of perhaps 10 to 14 to activate their individual processes and avoiding interfering with the door sequences, and other single number selections, built into FSX.
My problem arose with RC and GSX running and opening the Cargo doors for Boarding. The minute the number 2 in the Cargo door selection is depressed, the Cargo doors open, but RC also immediately responds with my ATC clearance. Again, by closing the Cargo doors, the minute the number 2 in the Cargo doors selection is depressed, RC also immediately responds to my apparent request for Pushback.
Thanks again for your thoughtful reply and belated Happy Holidays. John