“The Nikon D800 / D800E is not compatible with Eye-Fi X2 Cards.

Eye-Fi engineering has found and confirmed a compatibility issue with the Eye-Fi card that impacts the use of Direct Mode in the Nikon D800. We are currently investigating an issue with the D800’s SD slot that appears to contribute to a lack of steady signal while the Eye-Fi card is in Direct Mode which makes the Direct Mode feature incompatible with the camera. The Nikon D800/D800e passes all other wireless network tests and is compatible with wireless transfers via a wireless router.”

Eye-Fi Pro X2 16GB card available for pre-order At Amazon