Also same problem here.
My system was at 5.1U1a, if I try to upgrade to U2, SSO fails to start. I tried to upgrade to U1c and has been succesful, but again if I try to update to U2, fails the same way.
Any suggestions??? I don't want to do a fresh install again, that environment was fresh installed on April-May 2013... If I uninstall and install again I lose my database and config???
Regards.