Why you posted a question on the forum you already sent by email, which has been already replied to you ? Here's a copy of the reply you already got by email:
This is not a GSX problem, of course. It's caused by the scenery AFCAD. Some developers intentionally set the parking radius too small, even if it "looks right" visually, in order to play with AI assignments and prevent some AI to get there. Of course, GSX cannot possibly know if a parking is really small, or it has been set that way for some reason, since the AFCAD is the only thing GSX will "see" so, it doesn't have any other choice than to *trust* the AFCAD.
Of course, this can be fixed without editing the scenery, and the ability to do so has been there in GSX for years, with the "Max Allowed Wingspan" parameter, explained at Page 38 of the current manual.
There's no need to do it individually. All you need to do is do a single multiple selection of all gates you KNOWN are large enough for your airplane, then click the small "airplane" icon on the right of the "Max Allowed Wingspan", and it will automatically set all the selected parkings to be accepted for your currently loaded airplane so, it's just a single operation, only the first time you'll ever use an airport.