Tried via VPN still the same. Is it worth uninstalling gsx and re-installing?
Aren't you already trying to do that ? In any case, I looked your screenshot better and, the problem seems to be completely different: the installer got an "access denied" error when extracting a file, which can be caused by any of these:
- Antivirus blocking the installer, but you said it's already excluded.
- The simulator not being closed properly. But the FSDT Installer DOES check this and will refuse to run if MSFS is still running.
- The couatl engine still running. But the FSDT Installer DOES check this and will automatically terminate it in case it didn't close with the sim from the last session
- A permission problem in the Addon manager folder. But the FSDT Installer DOES check this and will automatically grant your user read/write permission on its folder.
Try to restart Windows and start the installer as the first thing you do and pay attention if you get the same error.