I Did all of that and added the line, but no joy. I still can't get GSX to work at Munich.
As I've said:
1) Be sure you have installed the latest Stand-Alone Addon Manager and then, after the first FSX launch after updating, choose "Restart Couatl and rebuild cache" from the Couatl Settings menu.
If still doesn't work, check if this AFCAD has no parkings. If it has no parkings, go back to step #1 because the current version of the program WILL automatically skip files with no parkings, provided you do ALL what has being said on step #1
If, instead, this AFCAD HAS some parkings, check its ICAO. If the ICAO is a fake one (I *assumed* it's MDDE, but I have no idea, since you haven't even said WHICH scenery you are referring to and there are several sceneries for EDDM out there), it WILL removed using the airport_visibility_MDDE = 0 in the [GSX] section of the Couatladdons.ini, which is a procedure fully documented in the manual.
If, instead, this AFCAD HAS some parkings, and its ICAO is EDDM, you don't have any other choice than remove it. GSX cannot obviously decide automatically between two airports files in the same place, with the same ICAO and with parkings in *both* of them, which one to choose.