Such dist-upgrade is not supported. This is allowed (and tested) from LTS to next LTS; and from n to n+1. All others cases are not tested nor supported, and are expected to fail. Indeed before upgrading, the system needs to be set back to 'genuine' status (purging ppa) ; which is the case with your installation.
** Changed in: ubuntu-release-upgrader (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/1606301 Title: Upgrade to Ubuntu 16.10 from 15.10 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1606301/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs