update manager is not woring Failed to download repository information

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http://askubuntu.com – My update manager is not working and showing this message Failed to download repository information Check your Internet connection. W:Failed to fetch http://ppa.launchpad.net/pmcenery/ppa/ubuntu/dists/precise/main/source/S... 404 Not Found , W:Failed to fetch http://ppa.launchpad.net/pmcenery/ppa/ubuntu/dists/precise/main/binary-i... 404 Not Found , E:Some index files failed to download. They have been ignored, or old ones used instead. Pleas help Thank you for your time. (HowTos)