Back up you phone and then click restore instead of update. That should get you sorted. Then restore from back up when iOS 5 is installed.
Tried that and it didn't work, gave me the same error.
Might have to abandon this for the day.
Back up you phone and then click restore instead of update. That should get you sorted. Then restore from back up when iOS 5 is installed.
My guess is there are too many doing it
Try later I say