Canon D40 Error code

Unfortunately, the ERR99 code is a catch-all code that means an UNKNOWN error has occurred. Because of this, it is going to be very difficult to pin down exactly what is causing the problem.

It could be a fault with either the camera (main circuit board, software, shutter mechanism etc.) or even the lens.

For starters, I would make sure that the lens electrical contacts are clean and the lens is mounted correctly and fully locked home. If you have a spare lens, try that also.

Next, I would reformat the memory card (do this in camera). If you have a spare memory card, try that also.

Check that the battery contacts are clean, and also the contacts of any external hardware such as vertical grips.

If none of these solve the problem, the only option left is to return the camera to Canon for a warranty repair, however if it is brand new, I would take it back to the store for an exchange.

Hope this helps,

Matt