Shutdown.exe, from the NT Resource kit, and Supplement 4, and from the W2K Resource kit, has a minor bug.
When you add a message of 8 character, or a multiple of 8 characters, it doesn't shutdown, and it displays: AdjustTokenPrivileges enable failed.
To get around the problem, adjust your message length.
shutdown.exe /L /R /T:20 "123456789" /Y
shutdown.exe /L /R /T:20 "12345678123456789" /Y