You use a non-official version of plymouth (plymouth 0.8.2-2-1mint3) which is holding back the upgrade. Please revert to official packages and try the upgrade again. I'm closing this report because it is not a bug with Ubuntu.
** 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/992041 Title: it is impossible to upgrade from 10.04 to 12.04 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/update-manager/+bug/992041/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs