OK I got it to work, although I still have to start COUATL64_MSFS by hand (it wont start automatically)
I unstinstalled ALL my FSDT products, including the P3D versions, deleted all FSDT folders (APPDATA, Addon Manager, etc.)
Upon loading FS20, GSX menu was there, but still was getting the message that couatl was not started, I started it by hand, and finally got GSX to work. Not sure if this will help anyone, but it is working for now. Umberto, how do I get COUATL to start automatically?