Symptoms: Trying to restore after a failed upgrade due to 1602/1604 errors etc, it's not working and you've tried the usual fixes.

1) Start a restore and wait till it gets to the "preparing to restore" progress bar and the iPhone screen goes black.
2) Kill itunes.exe in task manager.
3) Restart iTunes and say you want to restore / start the restore
4) Watch as iTunes magically overcomes the hurdle it was faceplanting at for the last 30 mins.

Post prompted by a "hmm, I'll just install the SMS fix before I go to bed". Yes, I should know better by now