I have some info that may be of help to some. If you are fortunate enough to have a prior version of GSX and want to install it, I have something that may help. First: turn off the internet connection, then run the install as administrator. Start FSX ( I cannot speak for other sim formats) Assuming you get a install prompt window DO NOT click on install. Click on "options" on the left side of the window and select install from there. If you should get the .dll error message say yes. Hopefully your prior version will now install. This worked for me. I realize all systems are different, so this may not help everyone. It seems we as consumers may have to work to help each other. Personally I think it would be nice for FSDT to at least post the prior major update once again so that at least some of us may succeed in installing it. As is often the case, denial runs rampant. It is our software, our add ons, our system. Anything but the developers fault. At this point I think most of us know better. Show us some support FSDT and solve the problem, or at least re offer the last version with fuel trucks etc. I really hope this helps some of you.
Blue skies,
Bill C