This error can have several causes, but a few basic checks are worth trying first:

• Make sure the battery is fully charged.
• Remove the battery for a while (even overnight), then reinstall it.
• Remove and reattach the lens, or try a different lens.
• Remove and reinsert the memory card, or try another card.
• Check whether the viewfinder is dark; if so, the mirror may be stuck up.

If the mirror is stuck, some users report gently nudging it down with a non-scratching tool, but this is risky and should be done very carefully.

If the error keeps returning, it often points to a shutter or drive mechanism problem. Some people attempt DIY repair by opening the bottom cover and lubricating gears or freeing the shutter motor, but community experience suggests this is usually temporary and can become impractical. Avoid that if the camera is under warranty.

If the simple steps above do not fix it, the safest recommendation is professional service through Nikon or a qualified camera repair shop.