I can't help you with a Nikon tech, but in case you don't have a manual here is what it says:
"Viewfinder -- Err blinks
Cause -- Malfunction detected
Remedy -- Release the shutter again. If the warning indication remains, or this warning appears frequently, contact authorized Nikon dealer or service center."
At the bottom of that page it also talks about low or poor batteries causing the camera to shut off. For that they write to turn off / turn on the camera. Or change the batteries.
I figure you've done the things, but maybe you haven't.