First, be sure you use the most current GSX version. If not sure, download it again.
If the problem still happens, check your scenery.cfg doesn't contain any errors, so the Aerosoft Schipol area is not read because of a problem in the scenery.cfg, even not in that area, but also elsewhere in the file. FSX is quite tolerant for errors in the scenery.cfg, but GSX requires that file to be clean.