The error is a problem with your memory card. You can try to format the memory card inside your camera instead of formatting it on a PC or Mac.
If you have formatted your memory card and the camera is still showing this message, the may be the card is not properly seated. So you have to take it out and put back in your D70.
If you have tried everything and you are still getting the same error, then there is either a contact problem inside the camera, or your memory card is damaged.