How to fix the Ubuntu GPG Error BADSIG

If you have got this error:

[COLOR="Red"][B]W: GPG error: http://archive.canonical.com intrepid Release: The following 
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key[/B][/COLOR]

when you try to use:

apt-get update

then there is two methods to fix this :

_Method 1:_ Run these commands one after another:

sudo -i
apt-get clean
cd /var/lib/apt
mv lists lists.old
mkdir -p lists/partial
apt-get clean
apt-get update

_Method 2:_ Run these commands one after another:

sudo aptitude -o Acquire::http::No-Cache=True -o Acquire::BrokenProxy=true update

sudo apt-get update

Thanks to [COLOR="Red"]ubuntu-geek[/COLOR]