If you downloaded GSX from an honeypot site (those site that will let you download FAKE "cracked" version, just to get you there and click on ads), it's no wonder it will cause issue with your FSX, since those wannabe pirates mess up by mixing files coming from old version, together with new versions, which is precisely what the software is designed not to allow...
They also do the same with PMDG airplanes: since they might not be able to crack new versions, they let you download a recent installer, with the gauge from the previous version (nobody notices, but the airplane will obviously malfunction)...
I'm not sure what the fake cracked version you have really does, but if you want to do a clean installation, do as follows:
- Uninstall GSX.
- Reply YES to the questions "Do you want to remove the Addon Manager?" and "Do you want to remove the Couatl scripting engine ?" made at the end. This is VERY important
- Check if your FSX\fsdreamteam\Couatl folder is not there anymore.
- Remove these folders:
%APPDATA%\Virtuali
%PROGRAMDATA\Virtuali
- Check you don't have any file named bglmanx* ( a .DLL and some .DAT files ) in your FSX root folder
- Reinstall GSX.