What to do about this?

[joe at actionline.com]

What to do about this?

W: A error occurred during the signature verification. The repository is
not updated and the previous index files will be used. GPG error:
http://security.ubuntu.com precise-security Release: The following
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic
Signing Key <ftpmaster at ubuntu.com>

W: A error occurred during the signature verification. The repository is
not updated and the previous index files will be used. GPG error:
http://archive.ubuntu.com precise-updates Release: The following
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic
Signing Key <ftpmaster at ubuntu.com>

W: Failed to fetch
http://security.ubuntu.com/ubuntu/dists/precise-security/Release
W: Failed to fetch
http://archive.ubuntu.com/ubuntu/dists/precise-updates/Release
W: Some index files failed to download. They have been ignored, or old
ones used instead.

=======
E: Encountered a section with no Package: header
E: Problem with MergeList
/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_precise-updates_main_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.
E: _cache->open() failed, please report.

=======
ERROR###ERROR###ERROR###ERROR###ERROR###ERROR###ERROR
E:Encountered a section with no Package: header, E:Problem with MergeList
/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_precise-updates_main_binary-i386_Packages,
E:The package lists or status file could not be parsed or opened.