Am reasonably familiar with updating firmware on both bodies and lenses but this issue is puzzling me.
When I try to update the firmware for my 400mm DO lens the rear screen on the camera goes blank and the top indicator flashes error 70. Removing and reinserting the battery is required to get the camera functioning again. I have tried 3 different sd cards, and the camera works fine the rest of the time. The problem only occurs when trying to do the firmware update.