@Crashdive Did you activate it the antivirus after the instalation of the gsx pro?
Not quite sure what you mean, but I'm using AVG Antivirus and created an exemption/exclusion for the whole Addon Manager folder.
I think (Umberto actually pointed this out) the mistake I made was I had the AV program completely disabled. Once I re-enabled it I then
followed your steps by un-installing and re-installing the GSX program and THEN creating the exemption/exclusion in AVG.
Fired up MSFS and BINGO! It worked.
One thing to notice (at least in my case): the couatl engine resided in the OS's System Tray but for some strange reason did NOT show
as an entry in the TaskManager. At least not straight away - only after activating the GSX menu from the toolbar within the sim did it show
up in the TaskManager. (Is that supposed to be like that? - I don't know. All I can say is it worked).
In other words: couatl started with the Sim (as defined within the exe.xml).
Maybe this will be helpful to other users facing the same or similar problems I had.
Regards, C