I've got the same problem and indeed `scanner' is a non-system group (created by hand) on my system.
% sudo addgroup --system scanner addgroup: The group `scanner' already exists and is not a system group. Exiting. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
