In manual mode 20 d is not caputuring the bottom 1/6 of the pic

When I take a photo in manual mode the bottom of the picture looks like I have something in front of the lens-it ends up looking like a black hazy area. It started during a photo shoot in my studio. Camera was not dropped. I originally thought it was my strap! It is not a clean line. It does not appear in any other of the modes and not on the auto mode. Lighting conditions do not matter. I have tried other lenses. Any ideas or suggestions would be greatly appreciated.
Thanks
Christie