[plug] Unable to lock passwd file when logged on as root

[Earnshaw, Mike]

List,

/<novice panic on>

Just tried to add a new user when logged on as root. Received message
that "unable to lock passwd file". I checked 'who' may be using the
system {only root}. Started to panic ... issued a fuser -u /etc/passwd
(?) got no information. PANIC, killed all process' using /etc/passwd and
was logged off. Logged back on and back to square one.

What should I check next. Help required please.

Thanks

Mike