I have been shooting with my Mark IV for about 2 years now and just recently been having a weird problem. I will shoot with the card and fill it up. Once I have no images left available, I take it out and put a new one in. However, when I put the new one in, the camera does not turn on right away and let me begin shooting. I usually have to take the battery out, put the battery back in and try that until it will read the card and I can start shooting again. Does anyone know why it would be doing this and if they have also had this problem? I don't remember it ever doing this when I first bought so just wondering if I may have something wrong with my camera.