I ran home from work and grabbed my Wimberly Gimbal and tripod.
I decided to preset my camera with what I thought would be the optimal settings when I got the dreaded message from the Nikon, ERR.
Shit. I quickly grabbed my phone and looked for online fixes. This had happened to me once before. It is a signifier of internal electronics problems.
I did everything they suggested. I changed the lens. I cleaned my contacts, in both the lens and camera with a microfiber cloth. I pulled out the cards and replaced the battery. I left the battery out for fifteen minutes. Nothing worked. I said goodbye to my hosts. There would be no shoot this evening. There was a trip to Kurt's Camera in my near future for a repair, if possible.
Now it has been hot and I had left the camera in a very hot car under a jacket. Could I have fried my very expensive Nikon D850? My god, not like I have the money right now to replace it.
I went home and kept searching and I found one guy who suggested a diagnosis and possible fix. Check the shutter button and see if it is functioning properly. I pressed the button, which was trapped in an imperceptible mid push and voila, everything now worked!
So anybody with this particular error code out there, check your shutter.