Hello!

When I refreshed my synaptic package manager I got this error message:

W: GPG error: http://archive.canonical.com maverick Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://extras.ubuntu.com maverick Release: The following signatures were invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key <ftpmaster@ubuntu.com>

W: GPG error: http://gb.archive.ubuntu.com maverick Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W: GPG error: http://packages.medibuntu.org maverick Release: The following signatures were invalid: BADSIG 2EBC26B60C5A2783 Medibuntu Packaging Team <admin@lists.medibuntu.org>
W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/maverick/Release

W: Some index files failed to download, they have been ignored, or old ones used instead.
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?
And since refreshing, I have been unable to install anything from the software centre - it keeps telling me I'm attempting to download unauthorised software.

Can anyone point me in the right direction for updating my authentication keys - bear in mind that I'm not an expert in Ubuntu!

Cheers ^_^