I have been shooting with a Nikon D800 and a new 24-70 f2.8 for about a month with no problems. Even had a full portrait session yesterday that went flawlessly. Then today I took out the combination to shoot my son's baseball game and the first shot sounded like the mirror stayed up and the camera showed err on the top lcd. I checked all of my settings and was shooting in aperture priority at iso100 in bright sunlight. The image displayed said it exposed at 1/320 at f5.6 but was very overexposed. I cycled power, removed the battery, and reseated the lens and still had the "err" on the lcd. Finally, I switched to manual and was able to clear the code. Then went back and continued to shoot in aperture priority with no further problems. Any thoughts as to the cause?