I'm a bit confused about that error.
I'm not sure what triggers it. It loads on the Upgrade Complete page. So I can tell you that the Uograde definitely worked!
But why is that function being called? It exists, but presumably listeners are disabled during upgrades. Thus the error. That function is called usually in a Cron Entry.
@
Mike: do Cron entries run during or at the end of the upgrade completing? If so I think something should prevent add on Crons from running while listeners are disabled during the upgrade process.