Zie hier een "goede" sources.list (voor Dapper, 6.06):
# Automatically generated sources.list
# http://www.ubuntulinux.nl/source-o-matic
#
# If you get errors about missing keys, lookup the key in this file
# and run these commands (replace KEY with the key number)
#
# gpg --keyserver subkeys.pgp.net --recv KEY
# gpg --export --armor KEY | sudo apt-key add -
# Ubuntu supported packages (packages, GPG key: 437D05B5)
deb http://nl.archive.ubuntu.com/ubuntu dapper main restricted
deb http://nl.archive.ubuntu.com/ubuntu dapper-updates main restricted
deb http://security.ubuntu.com/ubuntu dapper-security main restricted
# Ubuntu supported packages (sources, GPG key: 437D05B5)
deb-src http://nl.archive.ubuntu.com/ubuntu dapper main restricted
deb-src http://nl.archive.ubuntu.com/ubuntu dapper-updates main restricted
deb-src http://security.ubuntu.com/ubuntu dapper-security main restricted
# Ubuntu community supported packages (packages, GPG key: 437D05B5)
deb http://nl.archive.ubuntu.com/ubuntu dapper universe multiverse
deb http://nl.archive.ubuntu.com/ubuntu dapper-updates universe multiverse
deb http://security.ubuntu.com/ubuntu dapper-security universe multiverse
# Ubuntu community supported packages (sources, GPG key: 437D05B5)
deb-src http://nl.archive.ubuntu.com/ubuntu dapper universe multiverse
deb-src http://nl.archive.ubuntu.com/ubuntu dapper-updates universe multiverse
deb-src http://security.ubuntu.com/ubuntu dapper-security universe multiverse
# Ubuntu dapper-commercial repository
deb http://archive.canonical.com/ubuntu dapper-commercial main
# Seveas' packages (packages, GPG key: 1135D466)
deb http://mirror2.ubuntulinux.nl dapper-seveas all
# Seveas' packages (sources, GPG key: 1135D466)
deb-src http://mirror2.ubuntulinux.nl dapper-seveas all
Groet, Pjotr.