Why lately I've been getting this error when I try to update my computer? Ubuntu 12.04 Kernel 3.5.2 Processor i386 W:Failed to fetch http://ppa.launchpad.net/kernel-ppa/ppa/ubuntu/dists/precise/main/source/Sources 404 Not Found, W:Failed to fetch http://ppa.launchpad.net/kernel-ppa/ppa/ubuntu/dists/precise/main/binary-i386/Packages 404 Not Found, E:Some index files failed to download. They have been ignored, or old ones used instead.