CHA appears in window and camera will not work at

The very first thing which you should try is another CF card. Preferably a brand new one (not Lexar 80x, see below), but if not then use one which has been freshly reformatted in another Nikon DSLR.

ziggy53 on the Digital Grin forum posted an answer to this question two years ago. As I cannot put it any more clearly or succinctly his posting is reproduced as follows:-

"It appears that a Nikon D70/D70s CHA error is a general "cannot writeto card" error and can be caused by many different situations including:

1) CF card fault/failure
2) CF card fragmentation
3) CF connection, camera contacts
4) Camera internal failure with card write circuit board
5) Power supply in camera, potentially also related to the battery.

To rule out the Compact Flash card(s) as the fault, try a brand newcard (not Lexar 80x, as those seem problematic), format in camera anddo not field erase images. Reformat card in camera to start over. Ifthis procedure works, format the older cards in the camera and thenwork the cards by taking images, preferably RAW to fill up the card asquickly as possible. Do not completely fill the card but stop at around10 remaining images and format the card in camera once more. You mightbe good to go.

If these procedures don't work, it is recommended to return the camerato Nikon for a checkup. If Nikon cannot diagnose a problem, you mighttry a new battery as some claim a weak battery to be part of theproblem, but I don't see that "cure" mentioned often enough to know ifreally is a cure or not.

Repairs for an out-of-warranty repair for the problem relating to thecamera seem to run around $300USD from those few folks who reported acost."

All credit to ziggy53 http://www.dgrin.com/showpost.php?s=e7ff151930f88761a5feaa2e0348446c&p=710857&postcount=8

I've experienced this problem on a few D70 and D70s models and the advice ziggy53 gives has proven to be right on the mark; to Nikon's credit I've also found that in every case where I've definitely eliminated the possibility of a CF card failure they have attempted out of warranty repairs on a goodwill basis: all I had to pay for was for tracked and insured shipping to Nikon and they paid to return them. Of the five or six cameras which I've sent back so far only one had the problem re-emerge albeit in a less serious and very infrequent form. By then I'd given the camera to my niece and she's decided the fault is not serious enough to warrant sending it back again.