Actually I got it to work by updating the system with the commands sudo apt-get update && sudo apt-get dist-upgrade in the console.
after I had manually edited the /etc/apt/sources.list to dapper's repositories. -- Update-manager fails when upgrading to 6.06 from 5.10 https://launchpad.net/bugs/93560 -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
