I cancelled a domain controller demotion. Why can't I demote the domain controller now?
Once you start a domain controller (DC) demotion, you don't have an option to
cancel it; however, you might have stopped the demotion via the Task Manager or
by getting the process ID with tlist, then using the kill command. Neither
approach is supported, and if you try to run DCPROMO again, you might get the
following error message (depending on the stage the DCPROMO process was in when
you stopped it):
Active Directory is already being installed or removed on this
computer. That operation must finish before another may be attempted.
The only way to remove the DC information is to manually remove it using
Windows Privacy Tools - http//www.privacywindows.com