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I cannot upgrade my ubuntu from 13.04 to 13.10

This is error while i try to upgrade:

W: GPG error:  Release: The following signatures were invalid: KEYEXPIRED 1386276565
W: Failed to fetch  404  Not Found

W: Failed to fetch  404  Not Found

W: Failed to fetch  404  Not Found

W: Failed to fetch  404  Not Found

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

What have i tried already?

  1. Unchecked something like ..from CD-ROM.. on Ubuntu Software Center > Software Source.
  2. Tried to use this command "sudo rm -rf /var/lib/apt/lists/*"
  3. Tried to change download server

How can i solve this problem?

share|improve this question
up vote 1 down vote accepted

At some point you added an apt source for that natty-backports repository you see mentioned in your error. This repository is no longer available for some reason.

Find this; it will be either a line in /etc/apt/sources.list or a file in /etc/apt/sources.list.d. Then delete the line or the file, save, and try again.

share|improve this answer
"Some reason" being that natty reached end of life over two years ago. – psusi Jan 30 '14 at 19:38

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