Definitely the card. We've got 4 different digital EOS bodies at the office, and occasionally get this problem, but they've always been on the bargain CF cards (no name generics that were really inexpensive, but got replaced after quickly after a short history of corrupt file problems that formatting didn't seem to help). Had a few problems with Kingston CF cards, and Lexar cards too. Have yet to have a problem with the Sandisk cards in any flavor (ranging from the cheap no speed rated cards to the Extreme II's and III's). All our cards in the office are now Sandisk's-not worth the headache of lost chairside time when getting RAW images for accreditation cases.