I run FSX on 64-bit Windows 8.1, and it works fine for me. I have a lot of payware, and the *only* things I've had issues with are the Eaglesoft Cirrus SR22, and the RealityXP Flightline 'N' and 'T' gauges. All 3 of which use the Flight1 wrapper (and put license folders in the root of my C drive). Maybe that's a coincidence, but it seems unlikely. I was gonna buy the Flight1 GTN 750 for the RealAir v2 turbine Duke, but now I'm worried. AFAIK they do have a 30-day return period, so maybe I'll give it a go. Anybody know if it uses the same DRM system?