A likely cause is a power problem. If the battery voltage is too low or the battery is failing, the camera may start the shooting cycle but not complete it, which can trigger an “Err” message. The shutter/mirror mechanism needs relatively high power, so weak battery performance can show up this way.

First, fully charge the battery and try again. If the problem remains, test with another known-good, fully charged battery if possible. Also check the camera’s manual for the meaning of the “Err” display, since Nikon uses it for several issues, including low battery voltage or a memory-card-related problem.

If a fresh battery and basic checks don’t solve it, consult Nikon support or a repair center, as the camera may need service.