Update Manager no funciona

Hola Cuando trato de presionar el botón CHECK en Actualizado, no busco actualizaciones disponibles.

poniendo debajo del error.

"Failed to Download repository information"

Check your Internet connection..

W:GPG error: http://archive.canonical.com oneiric Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W:GPG error: http://archive.canonical.com lucid Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W:Failed to fetch gzip:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_oneiric_main_source_Sources  Hash Sum mismatch
E:Some index files failed to download. They have been ignored, or old ones used instead.

Ubuntu versión 11.10

Pruébalos en una terminal

sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update