debian squeeze backports

official site (link) statement

1) For squeeze add this line

deb http://YOURMIRROR.debian.org/debian-backports squeeze-backports(-sloppy) main

BUT do:
edit /etc/apt/source.list

add
deb http://YOURMIRROR.debian.org/debian-backports squeeze-backports-sloppy main
without "(.....)"

P.S.
check this link - http://backports-master.debian.org/Mirrors/ to find the nearest mirror.
Click on the link "debian-backports" in "ftp" column
You will get the page with content.
Some servers will have only wheezy backports.
Most of them will have folder named "squeeze-backports-sloppy" under dist folder.
Not squeeze-backports(-sloppy).

Good luck.