Few of us have found the ebay copy of GTS to be of help with the air systems. When I was going through my saga (
http://www.xoutpost.com/bmw-sav-foru...al-solved.html) of a speed dead sensor I accidentally calibrated one corner to be 1" higher than the rest. It was enough to tick off the system enough to go into in-active mode. There are also some other modes, line mode, transport mode that others have talked about needing to be reset from. The air systems seem to be a bit rarer but I can tell you GT1 software does a good job letting you see all of the inputs from sensors and calibrating too.
Do you have any warning lights on the dash too or only "sus inactive" on display?