I am getting this error message when trying to update.
W:Failed to fetch http://archive.canonical.com/commercial-ppa-uploaders/skype/ubuntu/dists/quantal/main/binary-amd64/Packages 404 Not Found [IP: 184.108.40.206 80] W:Failed to fetch http://archive.canonical.com/commercial-ppa-uploaders/skype/ubuntu/dists/quantal/main/binary-i386/Packages 404 Not Found [IP: 220.127.116.11 80] E:Some index files failed to download. They have been ignored, or old ones used instead.
And this error halts the updating process, so it never updates.
How to fix it?