This error message sounds like your plane is standing to far away for the jetway to be reached. Is your airplane configured for GSX and did you check the parking position of the Plane on the "modify parking" page? If the plane is standing on the right spot and the door is configured, it should work. Mabe you have the wrong door marked as the passenger entry.
I don't have the manual here, so I can't tell you where exactly to look, but it's for sure either wrong parking position or wrong door marked, so the jetway is out of reach.
