deb6 to deb7
/etc/apt/sources.list
deb http://security.debian.org/ wheezy/updates main
deb http://ftp1.us.debian.org/debian/ wheezy main contrib non-free
deb http://ftp1.us.debian.org/debian/ wheezy-updates main contrib non-free
apt-get update
apt-get dist-upgrade
apt-get install debian-archive-keyring