I have once, in the middle of a promo photoshoot for a local film maker. Are you using the battery grip?? Both shutter releases stopped working for me. I was freaking out, decided to take the battery grip off and use just the body only (only thing I could think of since taking out the batteries and restarting the camera didn't work.) only to realize that I didn't have the battery door with me. So I put the grip back on with the intention of using my remote, and it worked fine! Scary, and I have no idea what could have caused it, but haven't had that issue since then.