You wrote the update was only partial. - Have you tried a complete one? As in
Code:
sudo apt-get update
sudo apt-get upgrade
and maybe even
Code:
sudo apt-get dist-upgrade
(At least with Unity the Ubunty (12/14/16) dependency handling seems buggy.)
Have you checked that cups is not running any more before trying to restart it?
or something like
Code:
service cups status
Anything suspicious in the log files in /var/log/cups/ (especially error_log) right after (re)starting cups? (That's where they are on my Debian Sid. Most likely very similar on a *buntu.)