GSX works normally with the Airbus Extended X, since it's internally supported. You surely don't have to "reinstall" anything without even knowing *what's* causing it. The most likely cause it's some of your preference files corrupted, perhaps a GSX customization file for that airplane you made that has something wrong.
First, check if you have a Couatl.ERR file in your %APPDATA%\Virtuali folder. If you have it, post its content here.
If you don't, try to remove any custom configuration you made for that airplane, by removing every folder related to the Airbus Extended in the %APPDATA%\Virtuali\GSX\Airplanes folder. Also, check the main Airplane folder under FSX\Simobjects\Airplanes, and remove every GSX.CFG file you have there, if any. This will revert to use the configuration that comes with GSX.
Of course, I assume you use the very latest version of the GSX installer. If not, or not sure, download it again.