The problem doesn't have anything to do with GSX, of course. It seems GSX cannot find its objects, and this is usually caused by:
- A corrupted FSX.CFG, which the GSX installer couldn't update it with the lines containing the GSX objects paths, since the GSX installer won't try to touch an already corrupted FSX.CFG, which is usually the result of having edited by hand, but can also caused by bugged installers of other products.
OR
- Another product that has *reset* the FSX.CFG file to a previous version, one that didn't contained the lines added by the GSX installer. If this utility has a backup to restore from, it must be recreated *after* installing GSX, so it won't revert the file to a non-working version, in case it needs to reset it.
OR
- Wrong registry keys for FSX. You don't say which FSX you use but, assuming you use the Steam version, a very common problem of registry corruption is when you install the Steam version with the original FSX installed, then you removed the original FSX without reinstalling the Steam version. This would confuse proper products like GSX which supports both sims independently. The same problem could also happen if you use 3rd party utilities that in trying to "help" you installing add-ons not recognizing the Steam version, corrupts the registry to fool installers not compatible with Steam which, again, would confuse proper installers like GSX which supports both sims independently and must recognize them separately.