On 2014-05-31 regular support ended for Debian 6 "Squeeze", however Debian recently announced they are trialling Long Term Support (LTS) until 2016-02-06.
If you do not have a Gold or Platinum support contract with CWCS, you will need to alter the configuration of your server to enable the LTS updates.
Configure LTS Updates
Edit /etc/apt/sources.list and add the following lines for binary and source packages:
deb http://http.debian.net/debian/ squeeze-lts main contrib non-free deb-src http://http.debian.net/debian/ squeeze-lts main contrib non-free
You should also have the following enabled for LTS updates to work correctly:
deb http://http.debian.net/debian/ squeeze main contrib non-free deb-src http://http.debian.net/debian/ squeeze main contrib non-free
deb http://security.debian.org/ squeeze/updates main contrib non-free deb-src http://security.debian.org/ squeeze/updates main contrib non-free
deb http://http.debian.net/debian squeeze-lts main contrib non-free deb-src http://http.debian.net/debian squeeze-lts main contrib non-free
Finally, you should also check /etc/apt/apt.conf
If it contains the following line:
APT::Default-Release "squeeze";
Comment it out, or replace with:
APT::Default-Release "squeeze-lts";
Run Update and upgrade
Run apt-get update and apt-get upgrade to update and upgrade your system