I am having this problem too. I uninstalled the ubuntu-desktop package, the jaunty upgrade button appeared. I reinstalled ubuntu-desktop, and the error occurs again. There are consipicuous errors in the log file toward the end (attached).
** Attachment added: "See errors at bottom" http://launchpadlibrarian.net/24791659/apt.log -- update-manager can´t upgrade to jaunty https://bugs.launchpad.net/bugs/331280 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
