Using the command "ubuntu-bug ubuntu-release-upgrader" would have reported a bug with the necessary log files to determine what is wrong. Since you've already created a bug report in Launchpad you can use the command 'apport-collect 1247656' to add the log files to this bug.
** Changed in: ubuntu-release-upgrader (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1247656 Title: Fails to calculate upgrade setting software channels with custom ppas purged To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1247656/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs