GPG error

[calvinlyp]

hi all,

i got an GPG error when i reinstall my ubuntu 8.10

<error>
W: GPG error: http://sg.archive.ubuntu.com intrepid-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W: You may want to run apt-get update to correct these problems
</error>

this was in fact done in sudo apt-get update thus the suggestion from the terminal makes no sense.

i have read
http://ubuntuforums.org/showthread.php?t=145261
http://ubuntuforums.org/showthread.php?t=20506

but there is no complete answer to it.

below is my
cat /etc/apt/sources.list

#deb cdrom:[Ubuntu 8.10 _Intrepid Ibex_ - Release i386 (20081029.5)]/ intrepid main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://sg.archive.ubuntu.com/ubuntu/ intrepid main restricted
deb-src http://sg.archive.ubuntu.com/ubuntu/ intrepid main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://sg.archive.ubuntu.com/ubuntu/ intrepid-updates main restricted
deb-src http://sg.archive.ubuntu.com/ubuntu/ intrepid-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://sg.archive.ubuntu.com/ubuntu/ intrepid universe
deb-src http://sg.archive.ubuntu.com/ubuntu/ intrepid universe
deb http://sg.archive.ubuntu.com/ubuntu/ intrepid-updates universe
deb-src http://sg.archive.ubuntu.com/ubuntu/ intrepid-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://sg.archive.ubuntu.com/ubuntu/ intrepid multiverse
deb-src http://sg.archive.ubuntu.com/ubuntu/ intrepid multiverse
deb http://sg.archive.ubuntu.com/ubuntu/ intrepid-updates multiverse
deb-src http://sg.archive.ubuntu.com/ubuntu/ intrepid-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://sg.archive.ubuntu.com/ubuntu/ intrepid-backports main restricted universe multiverse
# deb-src http://sg.archive.ubuntu.com/ubuntu/ intrepid-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository. This software is not part of Ubuntu, but is
## offered by Canonical and the respective vendors as a service to Ubuntu
## users.
# deb http://archive.canonical.com/ubuntu intrepid partner
# deb-src http://archive.canonical.com/ubuntu intrepid partner

deb http://security.ubuntu.com/ubuntu intrepid-security main restricted
deb-src http://security.ubuntu.com/ubuntu intrepid-security main restricted
deb http://security.ubuntu.com/ubuntu intrepid-security universe
deb-src http://security.ubuntu.com/ubuntu intrepid-security universe
deb http://security.ubuntu.com/ubuntu intrepid-security multiverse
deb-src http://security.ubuntu.com/ubuntu intrepid-security multiverse


thanks in advance.