I am using FSX Windows 7.
Windows 7 is not supported anymore, and it's possible your problem might be caused by some Windows API calls we require that are not supported on Windows 7 by more recent versions of the Microsoft VC++ compilers, which we are required to use in order to keep compatibility with the latest SDK.
That doesn't mean we know for *sure* that Windows 7 won't work, but we don't test it, since nobody of us has Windows 7 anymore in years, mainstream support for it ended 4 years ago, and even the extended support will end next January.