What does card lock mean on a Canon A400 digital camera?

Card lock means that someone switched the little gray sliding lock on the memory card. It prevents the camera from saving new pictures to AND copying pictures from the card. All you have to do is take the card out and slide the little gray slider back into the unlocked position.

Hope that helps!

here's a review of them from ebays camera reviews & guides.

by card lock u can block the memory card so noone can change or modify pic in that memory card