I think this has been going on for a couple of years now, but I still get stuck trying to install
Ubuntu Restricted Extras to get the additional codecs needed for MP3 playback, etc. If you the install through the Software Center, it hangs up on a permissions screen in the background that you don't have any access to. Then you end up rebooting and get this annoying error pop-up:
The following packages requested additional data downloads after package installation, but the data could not be downloaded or could not be processed.
ttf-mscorefonts-installer
This is a permanent failure that leaves these packages unusable on your system. You may need to fix your Internet connection, then remove and reinstall the packages to fix this problem.
I got hit with this even now (February, 2016) with a new install of Ubuntu 15.10. Note to self: always remember to do this install from the command line:
sudo apt-get install ubuntu-restricted-extras
