Syntax error: unknown user ‘munin’ in statoverride file

Server running Ubuntu 12.04 lts

I installed munin the other day on a server. I decided later to remove it with apt-get.

I noticed that not everything was removed from the installation so manually removed the munin web directory and also removed the munin user-name and group from the sever.

However I have just now tried to run apt-get upgrade which is now returning an error:

dpkg: unrecoverable fatal error, aborting:
syntax error: unknown user 'munin' in statoverride file
E: Sub-process /usr/bin/dpkg returned an error code (2)

I am now out of my depth. What does this mean? Google results have not really been helpful.

Can anyone help?

Thanks,
John