Problem doesn't happen and hasn't been reported by anyone else.
If you are sure it's not corrupted files on your system, which can be easily verified by uninstalling/reinstalling the scenery (always use the most current installer, downloaded from our site), it might be a problem with your video driver and/or settings, or a problem with video memory corruption or exhaustion, either doing to other addons, or too high settings, or wrong tweaks applied, or simply bugs in your video driver.
- First try to reset your video driver settings to default. Be sure you don't use "Transparency Antialiasing" (or "Adaptive Anti-aliasing" ).
- 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 apply the HIGHMEMFIX tweak to the FSX.CFG, you can enabled it with the Addon Manager too, that's the only setting that really needs to be applied.