I ended up solving this myself simply through persisting. Dull and clunky process, but I ended up ignoring the "do not disconnect..." warnings. disconnecting it, and starting all over again.
Strangely, and I hope it's different for you, I now have a phone that confirms that it has the new firmware loaded up, but I see no discernible difference in performance, battery life etc etc. Close to a waste of time, if Nokia cares (which I don't think it does).