I would try these things before sending it in:
Turn on and do a system reset to factory defaults
Clean lens contacts
Error 99 is a catchall for any number of things, and not necessarily related to firmware. Could be anything.
I was shooting with a guy a few weeks ago and his Nikon just locked up on him when he depressed the shutter in the middle of a game. Nothing could get it started again. Ended up being a bad main battery and was fixed by buying a new battery the next day.