[Joe]

Hi there.
I've not had anything with the D2 bodies, but had exactly the same CHA error came up on the top plate LCD of a D1 body. It was more than a little worrying, as I thought it might have been a duff body. It only happened as it tried to write to the card
Like you though, I ditched the card (a 1gb Lexar one, ironically the only Lexar one I had) and stuck in a fresh card. all was well.
I tried replicating it by putting the card in another body, but it never came up with the error again. I think I binned the card (like you've found too....they have gotten so cheap to replace)
I've since thought it might have been related to the little button cell in the body, but since dismissed that idea.
I've even thought it might have been my fault in the way I used the card, ie, deleting photos directly off the card with the Laptop or desktop rather than back in the body.

To be honest though I let it pass as I never had the problem occur again with the D1h,D1x or either D2 bodies, and came to another possible reason that maybe it was because I continually buffered up to the max the original D1, so made the processor work hard (overheat??)..... so I'm glad you brought this back to light but on your D2.
Generally a bit of a mystery, so would be interested if anyone could shed some light??