As I've said, the only thing you must be sure, is the updated Addon Manager for FS9 is installed last. The problem might be related to:
- Using an outdated OS. We cannot guarantee anything older than Windows 8.1 will work. It *might* work with Windows 7, but we don't test it anymore, since it's completely unsupported by Microsoft since January.
- Not having updated the OS. Even if ( by pure chance ) the software might still work on Windows 7, you still need the latest updates ( which Microsoft won't release anymore ). I believe .NET 4.5.2 is the minimum version required.