Following situation: I tried to install skype wie the USC, but uninstalled it again since it was an old version and did not work correctly. So I installed Skype from skypes website.
But it seems like there is a problem with the old skype repository. The update manager wont update, apt-get gives error messages:

W:Failed to fetch http://archive.canonical.com/commercial-ppa-uploaders/skype/ubuntu/dists/quantal/main/binary-amd64/Packages  404  Not Found [IP: 91.189.92.191 80]

, W:Failed to fetch http://archive.canonical.com/commercial-ppa-uploaders/skype/ubuntu/dists/quantal/main/binary-i386/Packages  404  Not Found [IP: 91.189.92.191 80]

, E:Some index files failed to download. They have been ignored, or old ones used instead.

It seems to be a canonical repository missing/not working. When I try to activate the repository in the package manager it says I'm not allowed to, without asking for a password. I can't see how to activate them in the sources.list.

I'm on a fresh installed Ubuntu 12.10 computer, without any old or backuped data. My internet connection works without any problems. I can post this text, ping the ips given in the error messages, everything works. Except apt-get.

UPDATE
There seems to be an additional affection. I can't use auto-completion in terminal when I try to install something using "sudo apt-get install package-..." which is also really annoying.