Nikon has issued a statement regarding the lock up problems with the D4 and D800 and given a temp fix for avoiding the lock up issue.

Nikon has received reports of a small number of D4/D800 users who are experiencing ‘locking up’ issues, where the camera becomes unresponsive until the battery is removed and reinserted. Nikon is investigating a permanent solution to this issue and will update users accordingly. To immediately resolve this issue, users can turn off both the ‘Highlights’ and ‘RGB Histogram’ display options in the ‘Playback Display Options’ sub-menu found in the ‘Playback’ menu. Nikon apologizes for any inconvenience this may have caused users.

Have you encountered problems with your Nikon D4 or D800?

[via Nikon Rumors]