I had a customer who had trouble installing Windows 10 Fall Creator’s Update (Feature Update 1709) and who had Trend Micro antivirus. For some reason, Windows said it wouldn’t install because Trend Micro 2009 was installed. Some people have noted that Windows balks about other older versions. This link was a good start. But the problem remained.

What fixed it for me was to go to the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\UpgradeMigration, delete the file or folder listed, and then delete the registry key data. Most likely the update still won’t install normally. So I took a chance and choose the option to restart and update. That worked. So if you have an old program possibly causing issues, go to that registry key and then reboot and update instead of using the normal update way.