I made the experience that I had to tell apt-get which target release it should prefer. Usually I use a command like
Code:
apt-get -t testing dist-upgrade
for upgrading Knoppix. Sometimes some needed packages are still in the unstable or sid distribution. In that case I would use the command
Code:
apt-get -t sid install package
I think that the man pages are helpful
Code:
man apt-get
man apt_preferences