I have been uninstalling and reinstalling C++ runtime libraries trying to fix another issue with other P3D V3 programs and all of a sudden now I am getting these windows asking for activation of FSDT sceneries.
It's possible you removed a library that was required by our software, which is now not running correctly so, it thinks the scenery is not active. I guess you are missing the Couatl menu ? If yes, it's not starting because the things you did to the VC++ libraries.
The software requires the VC++ 2015 runtime library, and it gets installed automatically by any of our installers so, you should try doing that first.
If that doesn't fix it, uninstall every version of the VC++ 2015 runtime libraries, and reinstall any of our installers.
If that doesn't fix it, uninstall every version of the VC++ 2015 runtime libraries, then download them again from the Microsoft website, AND reboot Windows after installing.
https://www.microsoft.com/en-us/download/details.aspx?id=53587Download BOTH 32 and 64 bit versions, install both of them.
As far as I can understand the activations have a limit, so obviously this will be a problem after not many restarts of P3D V3. A window pops up for every FSDT scenery I have installed and GSX. How can I fix this please? And also can my activations be reset once this issue is solved?
This is not a problem. As explained many times on the forum, in the FAQ page, in the installation guide, an activation is consumed ONLY if you change hardware or reinstall Windows.