W: GPG error: http://archive.ubuntu.com hardy-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>

Try System > Administration > Software Sources > Authentication

and click on Restore Defaults.

Then open a terminal and
Code:
sudo apt-get update
.

If this doesn't work,in Software Sources,Change the Server to the Main Server and try again.

You might have to restore the Medibuntu repository after this.


Good Luck