At the 'Upgrading your system' screen, I first left the 'Customize packages
to be upgraded' button unchecked and pressed Next. Then I changed my mind
and went back and checked it. When I pressed Next I got:
Error mounting hda5: Device or resource busy
*** Bug 8850 has been marked as a duplicate of this bug. ***
*** Bug 9211 has been marked as a duplicate of this bug. ***
This is working in the latest development version.