可能的重复：
如何使用 PPA 修复 404 错误？
我无法删除桌面右上角的红色三角形。当我输入时，
sudo apt-get update && sudo apt-get upgrade
我收到以下错误消息：
W: Failed to fetch http://ppa.launchpad.net/michael-gruz/canon/ubuntu/dists/precise/main/source/Sources 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/michael-gruz/canon/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.
如何解决我的问题？