If the airplane you use doesn't have the ability to open a certain door, GSX can't fix this, the model itself has to be programmed with the door animation and that has to be tagged to either a default key command or a custom one. GSX can only be told *what* variable holds the door status, so it can check it.
If an airplane doesn't support the opening of a door, you will have to configure it in the GSX airplane configuration editor to be ignored (not removed), and GSX will allow the service to go ahead without checking the door's status. This will of course result seeing the catering man going through the fuselage, but if that door is static and just painted, that's to be expected.
