lists good sources
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Get:8 http://ca.archive.ubuntu.com quantal-updates/main amd64 Packages [79.5 kB]
Ign http://security.ubuntu.com quantal-security/universe Translation-en_CA
Ign http://ppa.launchpad.net quantal/main Translation-en
Err http://ppa.launchpad.net quantal/main Sources
  404  Not Found
Err http://ppa.launchpad.net quantal/main amd64 Packages
  404  Not Found
Err http://ppa.launchpad.net quantal/main i386 Packages
  404  Not Found
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lists more good sources
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Ign http://ca.archive.ubuntu.com quantal-backports/universe Translation-en_CA
Fetched 368 kB in 17s (20.7 kB/s)
W: Failed to fetch http://ppa.launchpad.net/team-xbmc/ppa/ubuntu/dists/quantal/main/source/Sources  404  Not Found

W: Failed to fetch http://ppa.launchpad.net/team-xbmc/ppa/ubuntu/dists/quantal/main/binary-amd64/Packages  404  Not Found

W: Failed to fetch http://ppa.launchpad.net/team-xbmc/ppa/ubuntu/dists/quantal/main/binary-i386/Packages  404  Not Found

E: Some index files failed to download. They have been ignored, or old ones used instead.