The crash can't possibly caused by GSX, since GSX can't crash FSX, because it runs outside of it (under the Couatl.exe program) and, an external .Exe, by definition, can't crash another one, not on Windows Vista/7/8 anyway.
It's likely your crash is the famous g3d.dll crash, which is the most common one in FSX, and it's usually fixed by installing the latest FSUIPC.