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Possible Duplicate:
How can I fix a 404 Error using a PPA?

I am trying to upgrade from 10.10 to 11.04. I have been getting these errors.

First one-

    Third party sources disabled

Some third party entries in your sources.list were disabled. You can re-enable them after the upgrade with the 'software-properties' tool or your package manager. 

Second one-

Error during update

A problem occurred during the update. This is usually some sort of network problem, please check your network connection and retry. 

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.
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marked as duplicate by Jorge Castro, hhlp, Ringtail, Tom Brossman, Mik Dec 9 '12 at 11:22

This question was marked as an exact duplicate of an existing question.

See also:… – Jorge Castro Dec 8 '12 at 21:13
The is for upgrading multiple versions: – oligofren Jun 6 '13 at 19:44

Natty is no longer supported IE: removed from the main server.

The .ISO can be found here but you will have to download and install a fresh copy or change your current repositories to include a local repository utilizing the CD as such.

Then upgrade via synaptic.

Try Press Alt+F2 and type in update-manager -d

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Try searching online for the .iso files download it and burn it to a cd like you where going to install ubuntu then put the disk in the computer and it will ask if you want to try to upgrade from it. Then you just have to click yes. You will have to do thus untill you get to a version that is supported

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Didn't I mention that? Oh, yeah! I think I did. – Ringtail Dec 8 '12 at 21:46

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