I am using Aerosoft Airbus X Extended ... I did rest and tried again and the same thing. I then restarted FSX and tried with stock plane and same problem. As soon as I call for a Service, Coualt disappears from the addon menus and i've noticed that the vehicles outside disappear too
Doesn't happen here, not with the Airbus nor with any other airplane, of course.
First, check you haven't installed a GSX.CFG custom configuration file for the Airbus X in its root folder ( the one under Simobjects\Airplanes ), because if you put a file there, the "Reset" option doesn't remove it.
If that doesn't work, perhaps you have a corrupted file in your preferences, which are NOT removed by uninstalling. To remove all GSX preferences, remove the %APPDATA%\Virtuali folder and REINSTALL.