11.04 - Updating ubuntu server apt-get gives me - 404 Not Found

I'm trying to update a Ubuntu server and when I run apt-get update I get a number of errors like the examples below (note I added some space after http).

Err http  ://no.archive.ubuntu.com natty/main Sources  404  Not Found
Err http  ://no.archive.ubuntu.com natty/restricted Sources 404  Not Found

AND

W: Failed to fetch http  ://no.archive.ubuntu.com/ubuntu/dists/natty/main/source/Sources  404  Not Found
W: Failed to fetch http  ://no.archive.ubuntu.com/ubuntu/dists/natty/restricted/source/Sources  404  Not Found

I tried to replace all occurrences of http   ://no.archive.ubuntu.com/ with http  ://archive.ubuntu.com/

But seems all of these archives are gone...

Version of Ubuntu:
lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 11.04
Release: 11.04
Codename: natty

How can I cleanup this mess?
Thanx for any help!
j

I assume the problem is because you are using a relatively old release of Ubuntu. A possible fix would be to open the /etc/apt/sources.list file with an editor of your choice
.Change all (xx.)archive.ubuntu.com to old-releases.ubuntu.com.. In your case an example would be ://archive.ubuntu.com/ubuntu/dists/natty/main/source/Sources becomes

://old-releases.ubuntu.com/ubuntu/dists/natty/main/source/Sources

after this, you can try running sudo apt-get update

For you to update your release,you need update-manager-core(sudo apt-get install update-manager-core) and then sudo do-release-upgrade but this will update you to the next release and has to be repeated until you reach say 12.04 LTS which has Long Term Support.