This has something to do with one of the PPAs that you have enabled, I suggest using ppa-purge to remove all of them.
** 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/1787862 Title: error "could not calculate the upgrade" while upgrading Kubuntu 17.10 to 18.04 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1787862/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs