Comment 9 for bug 1222654

I had the same problem on Ubuntu 14.04.01 LTS (incl. KDE).

I tried all three of Margaritas methods, but neither of them worked.

Then I completely removed the package from the system:
   sudo apt-get remove --purge ttf-mscorefonts-installer
and big surprise when I logged in again: -> The light bulb with the message was still there!

I found out that update-notifier is monitoring the contents of /var/lib/update-notifier/ and that the following file contains exactly the error message, update-notifier is complaining about:
    /var/lib/update-notifier/user.d/data-downloads-failed-permanently

My solution:

1. sudo mv /var/lib/update-notifier/user.d/data-downloads-failed-permanently /tmp/
2. login again and see whether you still have a bulb message
3. if you had removed the fonts package, install it again from a terminal window (don't use any GUI package installer, since they might conflict with the license agreement agreement dialog that comes with the package)