Apt-get failed to fetch from Ubuntu server with error code 404

I just updated from 10.04 to Oneiric and now I can not use my apt-get anymore. When I do I got the following error:

Ign http://security.ubuntu.com oneiric-security InRelease
Ign http://archive.ubuntu.com oneiric InRelease
Ign http://archive.ubuntu.com oneiric-updates InRelease
Ign http://security.ubuntu.com oneiric-security Release.gpg
Ign http://archive.ubuntu.com oneiric Release.gpg
Ign http://security.ubuntu.com oneiric-security Release
Ign http://archive.ubuntu.com oneiric-updates Release.gpg
Ign http://archive.ubuntu.com oneiric Release
Ign http://archive.ubuntu.com oneiric-updates Release
Ign http://security.ubuntu.com oneiric-security/main TranslationIndex
Ign http://security.ubuntu.com oneiric-security/multiverse TranslationIndex
Ign http://security.ubuntu.com oneiric-security/restricted TranslationIndex
Ign http://archive.ubuntu.com oneiric/main TranslationIndex
Ign http://security.ubuntu.com oneiric-security/universe TranslationIndex
Ign http://archive.ubuntu.com oneiric/multiverse TranslationIndex
Ign http://archive.ubuntu.com oneiric/restricted TranslationIndex
Ign http://archive.ubuntu.com oneiric/universe TranslationIndex
Ign http://archive.ubuntu.com oneiric-updates/main TranslationIndex
Ign http://archive.ubuntu.com oneiric-updates/multiverse TranslationIndex
Ign http://archive.ubuntu.com oneiric-updates/restricted TranslationIndex
Ign http://archive.ubuntu.com oneiric-updates/universe TranslationIndex
Err http://security.ubuntu.com oneiric-security/universe amd64 Packages
  404  Not Found
Err http://security.ubuntu.com oneiric-security/main amd64 Packages
  404  Not Found
Err http://security.ubuntu.com oneiric-security/restricted amd64 Packages
  404  Not Found
Err http://security.ubuntu.com oneiric-security/multiverse amd64 Packages
  404  Not Found
Err http://security.ubuntu.com oneiric-security/universe i386 Packages
  404  Not Found
Err http://security.ubuntu.com oneiric-security/main i386 Packages
  404  Not Found
Err http://security.ubuntu.com oneiric-security/restricted i386 Packages
  404  Not Found
Err http://security.ubuntu.com oneiric-security/multiverse i386 Packages
  404  Not Found
Ign http://security.ubuntu.com oneiric-security/main Translation-en_US
Ign http://security.ubuntu.com oneiric-security/main Translation-en
Ign http://security.ubuntu.com oneiric-security/multiverse Translation-en_US
Ign http://security.ubuntu.com oneiric-security/multiverse Translation-en
Ign http://security.ubuntu.com oneiric-security/restricted Translation-en_US
Ign http://security.ubuntu.com oneiric-security/restricted Translation-en
Ign http://security.ubuntu.com oneiric-security/universe Translation-en_US
Ign http://security.ubuntu.com oneiric-security/universe Translation-en
Err http://archive.ubuntu.com oneiric/main amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric/universe amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric/restricted amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric/multiverse amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric/main i386 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric/universe i386 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric/restricted i386 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric/multiverse i386 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/universe amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/main amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/restricted amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/multiverse amd64 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/universe i386 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/main i386 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/restricted i386 Packages
  404  Not Found
Err http://archive.ubuntu.com oneiric-updates/multiverse i386 Packages
  404  Not Found
Ign http://archive.ubuntu.com oneiric/main Translation-en_US
Ign http://archive.ubuntu.com oneiric/main Translation-en
Ign http://archive.ubuntu.com oneiric/multiverse Translation-en_US
Ign http://archive.ubuntu.com oneiric/multiverse Translation-en
Ign http://archive.ubuntu.com oneiric/restricted Translation-en_US
Ign http://archive.ubuntu.com oneiric/restricted Translation-en
Ign http://archive.ubuntu.com oneiric/universe Translation-en_US
Ign http://archive.ubuntu.com oneiric/universe Translation-en
Ign http://archive.ubuntu.com oneiric-updates/main Translation-en_US
Ign http://archive.ubuntu.com oneiric-updates/main Translation-en
Ign http://archive.ubuntu.com oneiric-updates/multiverse Translation-en_US
Ign http://archive.ubuntu.com oneiric-updates/multiverse Translation-en
Ign http://archive.ubuntu.com oneiric-updates/restricted Translation-en_US
Ign http://archive.ubuntu.com oneiric-updates/restricted Translation-en
Ign http://archive.ubuntu.com oneiric-updates/universe Translation-en_US
Ign http://archive.ubuntu.com oneiric-updates/universe Translation-en

I can ping any computer and access internet. sudo apt-get update and apt-get upgrade does not work (nor clean or autoclean), dpkg --configure -a does not help also. Any ideas?

Seems to me like a network issue, are you behind a proxy? If so, your configuration might be borked.

Have a look at your etc/apt/apt.conf file and check the proxy settings there.

(Added by user in question after discussing issue on comments)

SOLUTION
miguel@miguel-VirtualBox:~$ cat gedit /etc/apt/apt.conf
#Wrong!!!
#Acquire::http::Proxy "http://proxyconf/proxy.pac";
Acquire::http::Proxy "http://17X.XX.XX.X:8080";

It was an issue with the network settings - an invalid proxy was setup causing the problem.