Comment 9 for bug 202519

Did you reboot after the last set of updates?
I don't know your settings, so: set your apt mirror to main server from system > administration > software sources

The latest update I got was update-notifier:
$ apt-cache policy update-notifier
update-notifier:
  Installed: 0.70.6
  Candidate: 0.70.6
  Version table:
 *** 0.70.6 0
        500 http://archive.ubuntu.com hardy/main Packages
        100 /var/lib/dpkg/status

try reinstalling the ubuntu- packages:
sudo apt-get install --reinstall ubuntu-minimal ubuntu-standard ubuntu-desktop ubuntu-artwork
sudo apt-get -f install