Does the image show ok in the camera?
I didn't notice it until I was going through my images in Lightroom, so I don't know.
Hmm, that is two votes for memory card, I wouldn't have guessed that myself, having never experienced memory card errors before. I am using a pair of new Lexar 32GB 800X pro CF cards with my new body, since I always format the card after download, I have lost track of which card I was using for this frame. I will have to label them "A" and "B" and keep my eyes peeled for another such incident.
I have asked Canon support for help on this, and given them the link to this thread. I will share any insights that they might be able to generate.