Hi,
Forgive me if I have missed a thread with this solution already contained in it.
I did the Win 10 upgrade from Windows 7. Everything worked perfectly on Win 7 with FSX and FSDT. When the upgrade finished I stared FSX and it gives me the 'eSellerate ERROR -25007 Machine Mismatch. An hardware change has been detected and your activation will be verified now.'
I think it may have screwed up my REG or something? Not sure.
Would be happy to do a TeamViewer session as well/
Any help appreciated. If you need more info let me know.