I was upgrading from F13 to F14 by using preupgrade... I restarted and anaconda started the upgrade. When it was near at 80% an error happened, something like this: "anaconda had an error with VirtualBox-OSE, the installation will terminate" Then I got a text only mode and the only thing I could to is to reboot the system. Now I am with 80% F14 packets installed and the F13 packets to remove manually. I think that the problem caused by VirtualBox closed source version that I got from Oracle website. Maybe anaconda believed it was the VirtualBox-OSE from Fedora repositories... I don't have logs cause it was impossible to get any.
*** This bug has been marked as a duplicate of bug 650854 ***