A failure to regenerate the airport cache usually indicates a problem with one of your scenery files, usually a .BGL with 0 length.
Be sure you have Logging enabled in the Troubleshooting section of the GSX Settings, and on the next restart, you should have a Couatl.LOG in the %APPDATA%\Virtuali folder, which you can post ( ZIPPED, please ) here so I can confirm that is indeed the problem.