I am running the Update Manager (in Ubuntu 12.04) for the first time in several months. When checking for updates, the Update Manager doesn't find any, and returns the following error message:
W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/natty/main/binary-i386/Packages 404 Not Found, E:Some index files failed to download. They have been ignored, or old ones used instead.
What do I do to kick it up and running properly again?