When it's working, and you close FSX, open the Taskmanager and see if you still have a Couatl.exe process running after FSX has closed. If you have, terminating it manually will surely fix the problem.
It's possible that, due to other modules in conflict, it can't close together with FSX, another user for example found a problem caused by the GoFlight drivers, that prevented Couatl.exe to close, but with all the different modules out there, it can be something else too.