Q) Automatic Dark Scaling (Count 904) Warning – could not find a suitable definition of hot pixel threshold after 20 iterations. Turning Automatic Dark Scaling OFF

A) Neb is trying to find a threshold by which it can say there are a reasonable number of hot pixels that are hot but not saturated. If it can’t find such a threshold, it coughs up that error and then does normal subtraction. With normal subtraction, saturated hot pixels will show up as black holes. Your sky may be at 5000 but the hot pixel at 65535. That will leave the spot where the hot pixel was at 0, leaving that hole.

Q) Error reading data: 108

A) software is generating invalid FITS files