Upload & Sell: Off
Thank you all for your thoughts!
And yes Monito, I think you found the culprit: light getting past the seals in the card! :P haha!
But in reply to the serious side, I can rule out both of those for me: I had the card in and shooting for about another 45 minutes after that shot with no further problem, and I always format in-camera. Thank you for the ideas!
I really appreciate hearing about all the possible causes