Thanks Rick for your reply.
I installed the latest version of PI on my laptop, same result !
I also tried different images from my 2 cameras, no joy.
Long time user of PI with hundreds images, that does not exclude a basic operator mistake
It quits after demosaicing the first 4 images on my laptop which has 4 processors, and after 8 images on my main computer which has 8.
There was a major Win 10 update yesterday, so maybe...
How do I access Event Viewer ?