You cannot just enable pushback in both direction, and that will magically work. There might be a reason why a scenery developer might have set the parking spot with just one direction, or none at all.
Of course, GSX cannot possibly know if the scenery developer hasn't set a direction for a reason, or he might have simply forget to set one, that's why GSX can only trust the scenery but, that doesn't guarantee that, if you override that setting, it will always work correctly. In fact, it will work correctly only in those cases where the scenery developer didn't set the pushback direction because he made a mistake.
If there was a proper reason to disable the pushback in a specific place, overriding in GSX won't let the reason go away auto-magically! If there are no nodes in the AFCAD, for a reason (maybe there's an obstacle there), GSX cannot pushback over non-esisting nodes.
Read the GSX manual, the "Custom Pushback" chapter, and see if you can use a custom node by its coordinates instead. You'll have to open the scenery with ADE, to see which one might be the proper node to use, and get its coordinates to be inserted in GSX.
