Hi Don
Could you try this exactly if possible. Open Pixinsight from a reboot of the computer. Take a stacked(integrated) but unprocessed image, apply STF so you can see the image and then open DynamicPSF. I did this on 2 computers, one Windows 7 and the other Windows 10 and had no issue. Really want to try to help. I've just never heard of this happening in this manner when no other process is open.
Mike