The other day, while shooting for work, my ancient D1x got the dreaded CHA error. Luckily I already had enough shots to stitch my panorama together. I had a couple of extra CompactFlash cards, but one of them had problems of it's own, and the other was an equally ancient 128mb card that only holds 15 NEFs from the D1x.
I managed to get some of the most recent images off the card, but there was an another folder with several more images in it that my Mac wouldn't recognize. I could browse them with the camera though. While doing a little research into the CHA error, I ran across this thread at SportsShooter.com that mentioned Lexar Image Rescue. Then I found a two year old post on Fat Wallet for a free download of Lexar Image Rescue 3 for both Mac and PC, and the link still worked! It took more than half an hour, but it did the trick. Here's hoping it's just a bad card.