In a statement to PDN Online, Nikon USA has acknowledged a problem with "a small number" of D4 and D800 cameras. The affected cameras lock up during use and require the battery to be removed and reinserted in order to start working again. 

Nikon says it's working on a permanent solution and offers a temporary workaround in the meantime. In its note to PDN, Nikon says:

"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."

PDN came across the problem on their first review unit of the D4, and there have been reports of the problem from other reviewers and from some users on Internet forums.