What program do you have - Photoshop Elements 12/12.1 or Premiere Elements 12/12.1.
Somehow your thread got posted in the Adobe Premiere Elements Forum (video editing).
The Nikon D810 raw image was not supported until Camera Raw 8.6.
Photoshop Elements 12 shipped with Camera Raw 8.1 and covers to Camera Raw 8.5 camera support.
Photoshop Elements 13 ships with Camera Raw 8.6 and covers to Camera Raw 9.0 camera support (...can get to 9.1)
All that means is that you will need Photoshop Elements 13 with at least Camera Raw 8.6 to get support for your Nikon D810 raw files.
I just tried to use a Nikon D810 raw (nef) in Photoshop Elements 12 (Camera Raw 8.5)...does not work which is consistent with the above information. And, the Nikon D810 raw does work in Photoshop Elements 12 (which I have been able to update to Camera Raw 9.1).
1. Move to Photoshop Elements 13
2. Use the DNG Converter
Please consider, and give more details.