"Err" flashes. I was shooting (remote control) the finish line on a 10K race and about 400 shots in, once i reviewed the photos... I get one that has a lighter exposure band near the top half of the image.. Then, the next 10 images have what looks like a black diagonal line (out of focus) covering about half of the image.... then the next 600 photos are completely black. I took the lens off and looked inside... cleaned the electrical pins inside the camera, then watched the mechanism. The mirror up works, but there is a small black object at the bottom of the sensor inside the camera. I got my other (good) D300 and looked inside too, and it looks different without the black object at the bottom. The camera that has "Err" has 70,00 actuations. So....is this the kiss of death and therefore a shutter failure??