apt can't reach security.debian.org

[Luke L <rotgo54321@gmail.com>]

as root, I issue:

apt-get update

I get errors such as:
Err http://security.debian.org squeeze/updates/main amd64 Packages
  503  Forwarding failure

Is this something to worry about?

The relevant lines in my /etc/apt/sources.list are:
deb http://security.debian.org/ wheezy/updates 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

Thanks for any insight