Just purchased a Hasselblad 500c/m with A12 back. Was working just fine and then out of nowhere I was having troubles with the back. The film advance knob on the A12 keeps winding and winding but it's not advancing the frame counter. The '0' is half visible and stuck, and the window right next to it is neither white or red. When mated to the 500c/m (I have the 500 cocked before I place the A12 on) it fires; however, I am then unable to wind the film advance knob on the 500 again and I can't fire the shutter release as the colored dots on the 500 and A12 are not in sync. Any idea what the issue could be?