Bought my Nikon D70 in 2004, for no reason the error message CHA appears, twice I have managed to get it to go away after formatting my card, (10000 photos where taken on this card, bought a new 1GB Scandisk and have since taken 3100 photos with the new card), but on saturday it appeared again and refuses to go away, I had to format my card with another camera,who can help.
Check and replace the CMOS memory battery in camera. It will be a small watch-style battery. This battery is used to retain settings/menu choices. just a guess