I bought a Sigma 18-250 OS DG lens last month and it's a thing of lovelyness. Stuck it on the front of my 400D (Rebel XTi) and off I went. However, a couple of weeks ago, I was cheerfully snapping away when the camera just completely froze on me. The power light stays on, but nothing happens. It sounds like the shutter is up and stuck. The camera won't even turn off. Opening the battery door seems to reset everything, but I only get one or two more shots before it freezes again. Initially, I thought the problem was with the camera, but it only happens with this lens. I'm thinking it may be something to do with the OS system pulling too much power from the battery. Forgot to mention, I have the Double Battery Grip on there as well, the batteries are showing as full on the LCD (not convinced though, they do tend to pretend to be full, just before they go "OMG - I'm a flat battery) Has anyone else experienced this?