Hey .....
i guess i had the same issue.
It was fixed by adding a repository to the source.list file.
I cant remember which line it was but this is my current source.list :
deb file:/usr/pluto/deb-cache/ ./
deb
http://de.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
deb-src
http://de.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
deb
http://de.archive.ubuntu.com/ubuntu/ precise-updates main restricted universe multiverse
deb-src
http://de.archive.ubuntu.com/ubuntu/ precise-updates main restricted universe multiverse
deb
http://de.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src
http://de.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb
http://security.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
deb-src
http://security.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
deb
http://deb.linuxmce.org/ubuntu/ precise unstable
deb
http://deb.linuxmce.org/ precise main
deb
http://debian.slimdevices.com/ stable main
deb
http://archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
deb
http://archive.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
deb
http://archive.canonical.com/ubuntu/ precise partner
deb
http://download.videolan.org/pub/debian/stable/ /
deb mirror:/mirrors.ubuntu.com/mirrors.txt/ precise universe main
Cheers,
Ochorocho