This has been discussed in many other threads, and it's not a GSX problem, but a video/fsx setting gone wrong.
- First try to reset your video driver settings to default. Be sure you don't use "Transparency Antialiasing"
- If that doesn't work, try to update your video driver too.
- If that doesn't work, try to reset your %APPDATA%\Microsoft\FSX\FSX.CFG file, to have FSX rebuild a new one with default settings, be sure you have the "Advanced Animation" option enabled
- If that doesn't work, try to "Repair" your Acceleration or SP2 installation, this has fixed the problem for some users.