ERROR_NOT_ALL_ASSIGNED when using "Shutdown computer when finished"

[Xyzzy]

Using "shutdown.exe /s /f" the result is that nothing happens and the last log line is:
[15.11.2020 22:22:50] Run program/action "shutdown.exe /s /f"

If I run "shutdown.exe /s /f" from a command line (my account - standard user), I get a Windows dialog "You will be logged out in a moment. Windows will be closed in less than a minute.". Then after a short time system is shut down.