Invalid sig files in Update Manager, etc.

Lubuntu 11.10 LXDE desktop, 3.0.0-14-generic-pae (i686)

Update Manager is showing that I have not run updates for last 44 days,
which is not correct.

Not a whiz at Linux, but ran sudo apt-get update in a terminal, and came
back with a lot of invalid sig errors, and failure to fetch HTTP sources.

"Reading package lists... Done
W: A error occurred during the signature verification. The repository is not
updated and the previous index files will be used. GPG error:
http://au.archive.ubuntu.com natty-backports Release: The following
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic
Signing Key <ftpmaster@ubuntu.com>

W: GPG error: http://packages.medibuntu.org oneiric InRelease: The following
signatures couldn't be verified because the public key is not available:
NO_PUBKEY 2EBC26B60C5A2783
W: A 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 oneiric Release: The following signatures were
invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key
<ftpmaster@ubuntu.com>

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://ppa.launchpad.net oneiric Release: The following
signatures were invalid: BADSIG DF8030F05ED1D082 Launchpad PPA for Claws
Mail
W: GPG error: http://ppa.launchpad.net oneiric Release: The following
signatures were invalid: BADSIG 7B1AB59047B4D1C4 Launchpad qbittorrent
W: GPG error: http://ppa.launchpad.net oneiric Release: The following
signatures were invalid: BADSIG 34C08E07CF3D9164 Launchpad PPA for
Alessandro Lanave
W: GPG error: http://archive.ubuntu.com oneiric Release: The following
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic
Signing Key <ftpmaster@ubuntu.com>
W: GPG error: http://ppa.launchpad.net oneiric Release: The following
signatures were invalid: BADSIG 53D9CF3EE3B3D1B9 Launchpad PPA for PhobosK
W: GPG error: http://ppa.launchpad.net oneiric Release: The following
signatures were invalid: BADSIG D2B5F4E7C3BB95BB Launchpad Gstyle PPA
W: A 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 natty Release: The following signatures were
invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key
<ftpmaster@ubuntu.com>

W: GPG error: http://archive.canonical.com natty Release: The following
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic
Signing Key <ftpmaster@ubuntu.com>
W: GPG error: http://ppa.launchpad.net oneiric Release: The following
signatures were invalid: BADSIG 6AF0E1940624A220 Launchpad PPA for TualatriX
W: GPG error: http://ppa.launchpad.net oneiric Release: The following
signatures were invalid: BADSIG DFB844B8BB91632D Launchpad PPA for Weather
Indicator Team
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 oneiric-backports Release: The following
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic
Signing Key <ftpmaster@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 oneiric-proposed Release: The following signatures
were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key
<ftpmaster@ubuntu.com>

W: Failed to fetch http://au.archive.ubuntu.com/ubuntu/dists/natty-
backports/Release

W: Failed to fetch http://extras.ubuntu.com/ubuntu/dis...ic/Release

W: Failed to fetch http://extras.ubuntu.com/ubuntu/dis...ty/Release

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/oneiric-
backports/Release

W: Failed to fetch
http://ppa.launchpad.net/lxde/ppa/u...in/binary-
i386/Packages 404 Not Found

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/oneiric-
proposed/Release

W: Failed to fetch http://ppa.launchpad.net/mozillateam/thunderbird-
stable/ubuntu/dists/oneiric/main/binary-i386/Packages 404 Not Found

W: Failed to fetch
http://ppa.launchpad.net/tualatrix/...in/binary-
i386/Packages 404 Not Found

W: Some index files failed to download. They have been ignored, or old ones
used instead"

Looks like a mess, how to fix?

As usual, Thanks in Advance!