When I try to update, I get this error: Failed to Download your repository information Check your internet connection W:GPG error: http ://ppa.launchpad.net oneiric Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4874D3686E80C6B7, W:Failed to fetch http://ppa.launchpad.net/pmcenery/ppa/ubuntu/dists/oneiric/main/source/Sources 404 Not Found W:Failed to fetch http://ppa.launchpad.net/pmcenery/ppa/ubuntu/dists/oneiric/main/binary-i386/Packages 404 Not Found E:Some index files failed to download. They have been ignored, or old ones used instead.