First, check which AFCAD GSX is using, which can be done using the scenery customization dialog, and be sure the AFCAD in use is the one that comes with the 3rd party scenery you are using. If it's not, try to force a complete scenery cache rebuild, by removing the following folders ( with FSX CLOSED!! )
c:\ProgramData\Virtuali\Couatl
c:\ProgramData\Microsoft\FSX\SceneryIndexes