Fetched 841 kB in 28s (29.3 kB/s) W: GPG error: http://packages.mate-desktop.org raring Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 68980A0EA10B4DE8 W: Failed to fetch http://ppa.launchpad.net/pmcenery/ppa/ubuntu/dists/raring/main/binary-i386/Packages 404 Not Found E: Some index files failed to download. They have been ignored, or old ones used instead. userx@bw:~$ How do I fix that? How do I add a PUBKEY to get needed files to complete install of Cinnamon?