GPG Error / NO_PUBKEY Debian 6.0 Squeeze

If you encounter the following error when updating, I listed below the steps to fix it.

"W: GPG error: http://security.debian.org squeeze/updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA"

1. check all the keys installed on your server for debian repository.
$apt-key list

2. Install the debian-archive-keyring.
$apt-get install debian-archive-keyring

#You should be able to see the following:
pub 4096R/B98321F9 2010-08-07 [expires: 2017-08-05]
uid Squeeze Stable Release Key

pub 1024D/F42584E6 2008-04-06 [expires: 2012-05-15]
uid Lenny Stable Release Key

pub 4096R/55BE302B 2009-01-27 [expires: 2012-12-31]
uid Debian Archive Automatic Signing Key (5.0/lenny)

pub 2048R/6D849617 2009-01-24 [expires: 2013-01-23]
uid Debian-Volatile Archive Automatic Signing Key (5.0/lenny)

pub 4096R/473041FA 2010-08-27 [expires: 2018-03-05]
uid Debian Archive Automatic Signing Key (6.0/squeeze)

3. Update your Debian server now.
$apt-get update


Another Case:
Incase you encountered the error below.
"W: GPG error: http://www.debian-multimedia.org testing Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 07DC563D1F41B907"

Fix:
$apt-get install debian-multimedia-keyring

3. You can now execute your update
$apt-get update

If it doesn't work try this!

rm /var/lib/apt/lists/* -vf
apt-get clean
apt-get update


Another Case:

W: GPG error: ftp://ftp.deb-multimedia.org squeeze Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 07DC563D1F41B907
W: GPG error: ftp://ftp.deb-multimedia.org squeeze-backports Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 07DC563D1F41B907


Fix:
#Insert below in your /etc/apt/sources.list.

deb ftp://ftp.deb-multimedia.org squeeze main non-free
deb ftp://ftp.deb-multimedia.org squeeze-backports main


Console:
#Add Key
apt-get install debian-keyring
gpg --keyring /usr/share/keyrings/debian-keyring.gpg -a --export 07DC563D1F41B907 |apt-key add -



Another Case:
"W: GPG error: http://nginx.org squeeze Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY ABF5BD827BD9BF62"

Fix:
#Insert below in your /etc/apt/sources.list.
deb http://packages.dotdeb.org stable all

Console:
#Add Key
gpg --keyserver keyserver.ubuntu.com --recv-key ABF5BD827BD9BF62
gpg -a --export ABF5BD827BD9BF62 | apt-key add -
apt-get update


Another Case:

W: GPG error: http://packages.dotdeb.org stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY E9C74FEEA2098A6E

Fix:
#Insert below in your /etc/apt/sources.list.
deb http://packages.dotdeb.org stable all

Console:
#Add Key
wget http://www.dotdeb.org/dotdeb.gpg
cat dotdeb.gpg | apt-key add -
rm dotdeb.gpg

sources.list for Debian Squeeze 6.0

deb http://ftp.de.debian.org/debian/ squeeze main non-free
deb-src http://ftp.de.debian.org/debian/ squeeze main non-free

deb http://security.debian.org/ squeeze/updates main
deb-src http://security.debian.org/ squeeze/updates main

deb http://ftp.de.debian.org/debian/ squeeze-updates main
deb-src http://ftp.de.debian.org/debian/ squeeze-updates main

deb ftp://ftp.deb-multimedia.org squeeze main non-free
deb ftp://ftp.deb-multimedia.org squeeze-backports main

deb http://nginx.org/packages/debian/ squeeze nginx
deb-src http://nginx.org/packages/debian/ squeeze nginx

deb http://packages.dotdeb.org stable all