Comment 4 for bug 67348

It turns out I had versions of libgl1-mesa{,-dri} installed that were newer than what edgy itself provided (maybe I got them from a compiz repository?)

When I downgraded these from 6.5.1+cvs20060824 to 6.4.1-0ubuntu8 (dapper's latest), update-manager was able to proceed further to a dialog stating: "Do you want to start the upgrade?".