Does the installation of GSX place the FSX default airport vehicles so to speak in limbo, as some sort of inactive or backup file? I ask because I recently got a mission that wouldn't run on my computer although it worked for others. It turned out that two library objects in the .xml file (push back blue and platform lift blue) weren't found on the computer by the mission. After removing these two objects from the .xml file, the mission ran as it should.
Cheers,
eskil