The problem doesn't have anything to do with GSX which, instead, is telling you an useful information, that your DLL.XML or EXE.XML file in your %APPDATA%\Lockheed Martin\Prepar3D folder is corrupted, most likely because you have hand edited them, or another add-on has corrupted them, so it’s missing a correct XML closing tag.
If you could send me the files, I can fix them for you. Do not post the files directly, but ZIP them together first, and "Attach" them to a message.