Are you able to run apt-get update?
Yes. The problem is with dpkg or debconf. When using synaptic, it said that debconf was broken.
An update:
# dpkg-reconfigure debconf
dpkg-query: parse error, in file `/var/lib/dpkg/available' near line 359695 package `dcgui':
field name `
/usr/sbin/dpkg-reconfigure: debconf is not installed
But, when I apt-get install debconf
debconf is already the newest version.
What do you make of this?