Troypiggo suggested I post my question about Bpp here.
I had some problems using this tool but after trying a couple of times, I managed to find the error I made.
Instead of using prestacked master bias and flats (from DSS), I let the tool make these master files from scratch.
But now I have another problem. While trying to figure out what went wrong the first times, I used stacks of about 10 images for bias, darks, flats and lights. And that worked fine.
Now, when I try to stack more than about 25 lights, the process ends up not finding enough matching star pairs. And after 25 retries I had to manually abort the process.
Is there a way of using some sort of parameter to end this, after say 10 tries and move on to the next image? I used several different reference images so I don't think that will be the problem.
Or is it possible to make stacks of 20 lights and stack these stacks, if you understand what I'm trying to say ?
I really want to use PI for the entire process, not only post-processing. And using the information on this forum I'm quite confident, that will be possible.