In recent weeks, I’ve encountered multiple machines unable to install Windows Updates thanks to a perpetual message claiming:
No matter what the user does, these machines simply won’t install any updates.  If they’re rebooted as requested, nothing happens, and the message simply reappears upon reentering Windows, no matter how quickly the user attempts to invoke the process.  Resetting the SoftwareDistribution repository, by the way, does not solve this problem.  Neither does restoring the conventional Windows Update settings using a variety of troubleshooters, such as the Microsoft troubleshooter.
What does work, however, is removing a single registry key which is responsible for the problem:
(apologies for high-res screenshots; I’m too lazy to correct this)
The particular key in question is:
- HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update\OSUpgradePendingReboot
All that’s necessary is to delete this key, and the problem evaporates, like it never even happened!  The key is related to the Windows 10 in-place upgrade process which (used to) take place through Windows Update.  The situation seems to suggest that these machines were nearing the final stages of the upgrade when something happened and they failed to install it.  Now, the upgrade windows has officially passed.
As always, of course, it’s wise to create a System Restore point before modifying your registry, etc., yada yada.
Hope this helps!