From your description it seems there's a conflict between Fspassengers and GSX.
The most likely cause might be a problem with conflicting Visual C++ runtime libraries. The system ( called Side-by-side loading ) is designed to allow different programs using different versions of the same libraries to run at the same time. This in theory, but sometimes the whole (very complex) mechanism doesn't work.
You might *TRY* to download and install the latest Couatl 3 Public Beta AFTER GSX, which uses the VC++ 2013 runtime library, which is hopefully more supported, maintained and bugfixed. GSX will soon include it as standard in the official version anyway.
http://www.fsdreamteam.com/forum/index.php/topic,11796.0.htmlThis, assuming the problem IS caused by a runtime libraries conflict, which seems to be the most likely cause, but it's surely not the only possible one.