This seems to happen as the beginning when I am setting up a flight, if I hit the menu bar FSX crashes. If I stop the Coutl process then no problem. Is this a known issue ?
The Couatl process doesn't have any ability to crash FSX, since it's an external .EXE so, there's no way it can affect it. However, that FSX is prone to crashing when accessing its menu, it's very well known, look for all forums for the uiautomationcore.dll problem, you will find plenty of reports, well before GSX was released.
This seems to happen at any airport although to be specific it happened yesterday at EGLL payware, gate 421, with ConcordeX, and an airport where I have AES. I had not even started GSX when this occured.
Fact you haven't started GSX, clearly indicates the problem doesn't have anything to do with it. No GSX code is running, until you start its menu.
One other problem I noticed is that with ConcordeX, GSX seems to inhibit the FSLabs ground power even though it has not been started.
GSX doesn't affect in any way any airplane, since NO airplane interaction is made with writing variables. GSX only READS values from an airplane, so it's not possible it could affect it.