Comment 5 for bug 1063099

Interesting. You seem to have repositories of Natty, Oneiric and Precise in your sources.list which is certain to cause some issues. I don't really have any idea what could've caused this. Have you done any distribution upgrades lately?

The only way to fix the broken sources.list is to manually replace your current sources.list with the default one and hope nothing breaks. To do that, please refer to the following Ask Ubuntu answer:
http://askubuntu.com/questions/124017/how-do-i-restore-the-default-repositories#124024