Please run the following command in a terminal and copy&paste the output here:
apt-cache policy update-manager Try to reinstall update-manager: sudo apt-get install --reinstall update-manager/dapper -- Cannot open Repositories panel in Synaptic Package Manager https://launchpad.net/bugs/50441 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
