OK, closing this bug report since you said it works now. (In case this happens again, the problem is due to the fact that package lists are not downloaded correctly - just update them again and you should be fine).
** Changed in: update-manager (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1033638 Title: Requires installation of untrusted packages. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/update-manager/+bug/1033638/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs