The message about no valid AFCAD is usually caused by using external scenery configurators from 3rd party airports that switch between different AFCAD files and, depending on the method they do to switch ( copy or rename ), GSX might not be able to automatically detect a change in the AFCAD file, because in order not to slow down the start up too much, GSX doesn't check each and every file in your sim, but only the last modification date of all the scenery folders.
That's the reason why there's a "Restart and rebuild the airport cache" option in the Couatl settings menu: so you can force a rebuild of the airport cache after you switched the AFCAD file for an airport and it wasn't detected automatically.
