The debian-volatile project has been discontinued with the Debian Squeeze release

Please replace line "deb http://ftp.debian.org/debian squeeze-updates main" in /etc/apt/sources.list with "deb http://ftp.debian.org/debian squeeze-updates main"

Source: http://www.debian.org/volatile/ http://lists.debian.org/debian-volatile-announce/2011/msg00000.html