Someone here MUST have had this issue at some point - I can update my debian installation (and upgrade it), but I just recently added the non-free repository to the list, so I can download jdk6. When I try to update aptitude after adding the line, I get the following errors:

root@node:~# vi /etc/apt/sources.list
root@node:~# aptitude update
Err http://security.debian.org squeeze/updates Release.gpg
  Could not resolve 'security.debian.org'
Err http://security.debian.org/ squeeze/updates/main Translation-en
  Could not resolve 'security.debian.org'
Err http://security.debian.org/ squeeze/updates/main Translation-en_US
  Could not resolve 'security.debian.org'
Err http://ftp.us.debian.org squeeze Release.gpg
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze/contrib Translation-en
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze/contrib Translation-en_US
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze/main Translation-en
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze/main Translation-en_US
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze/non-free Translation-en
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze/non-free Translation-en_US
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org squeeze-updates Release.gpg
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze-updates/main Translation-en
  Could not resolve 'ftp.us.debian.org'
Err http://ftp.us.debian.org/debian/ squeeze-updates/main Translation-en_US
  Could not resolve 'ftp.us.debian.org'

Here is my "sources.list" file:

root@node:~# vi /etc/apt/sources.list
#

# deb cdrom:[Debian GNU/Linux 6.0.0 _Squeeze_ - Official Multi-architecture amd64/i386 NETINST #1 20110205-14:45]/ squeeze main

#deb cdrom:[Debian GNU/Linux 6.0.0 _Squeeze_ - Official Multi-architecture amd64/i386 NETINST #1 20110205-14:45]/ squeeze main

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

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

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

deb http://ftp.us.debian.org/debian/ squeeze main contrib non-free

_________________
Up and coming Debian Linux server admin

I'm just guessing, but which data center is your node in, and what's your /etc/resolv.conf? It could be a simple DNS resolver issue.

Also, what happens if you run "host ftp.us.debian.org"?

_________________
Matt Nordhoff (aka Peng on IRC)