On an older Nikon D40x, this message usually points to a mechanical or power-delivery problem rather than a setting issue.

Based on the shared fixes, two likely causes are:

1. A sticking shutter/mirror mechanism — If turning or lightly lubricating the bottom shutter drive wheel makes it work temporarily, that suggests something in the shutter or mirror actuation may be binding.
2. Intermittent battery contact — Weak or dirty battery contacts, or a battery door that no longer holds firm pressure, can cause startup or shutter-cycle errors. Cleaning the contacts and checking whether pressure on the battery door changes the behavior is worth trying.

Practical things to check:

• Clean battery and camera contacts carefully.
• Test whether pressing the battery door inward changes anything.
• Remove and reinsert the battery.
• If the camera only recovers briefly after moving the shutter wheel, the internal mechanism is likely failing.

Because the camera is quite old, recurring errors after these checks usually mean a worn mechanical part or unreliable contact that may need professional repair. Be cautious with improvised lubrication, as excess can damage other parts.