I don't think it's your memory cards causing the problem. I recently started using 16gb Kingston Ultimate 600x cards with my D800, 700 and 300s and they work perfectly. I also use Kingston Elite Pro 4 and 8gb 133x cards and they work perfectly. I like the 16gb Ultimate so much that I'm thinking about getting their 32gb CF cards. The Ultimates from my testing is as fast as my Sandisk Extreme cards. Good luck with your camera. Let us know what the problem was.