Update Manager not starting

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http://askubuntu.com – I get this after the Update Manager said "Check your Internet Connection" W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/main/source/Sources 502 Bad Request [IP: 80] , W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/main/binary-i386/Packages 502 Bad Request [IP: 80] , E:Some index files failed to download. They have been ignored, or old ones used instead. (HowTos)