I have attached the .BGL to this reply. Thanks for your help!
As I've suspected, that .BGL is not using the standard .BGL format: I guess it's probably encrypted.
This means, it will never be possible to use it with GSX, or any other utility (maps, flight planners, etc.) that might need to read the AFCAD data, and of course you won't even be able to edit it yourself using ADE or AFX.
There's just nothing we can do to fix this, your only option is to contact the original scenery developer, and ask if they can supply you with an unencrypted .BGL, possibly suggesting that, if they want to use file encryption (we use it too, for some files), it's not a good idea to encrypt the AFCAD file too.