As was discussed already on the forum, this is not a GSX problem, but a video driver problem or a problem with a video driver setting, or a problem with your FSX.CFG settings. Try all the following:
- Update your video driver
- Reset your video driver settings to default
- Reset the FSX.CFG to default, by removing the %APPDATA%\Microsoft\FSX\FSX.CFG file
- After you reset the FSX.CFG file, be sure the HIGHMEMFIX tweak is set to 1 (you can set it directly with the Addon Manager)