<quote>"mask is full" means that your mask is "full white" after cropping. </quote>
Ah! I understand now.
From looking at the source, I could see that it should only say "Mask full" if the mask was 100% white, but my mask isn't (I thought)... but I was overlooking the "after cropping" detail.
For my first experiments, I'm using a simple white rectangle against full black as my mask, and in my keenness for speed, I see that with my loc="" string I've cropped well inside the white rectangle.
<quote>Have you tried Load_Stdcall_PluginM</quote>
Not yet. I'll try the newer version with that later.
Thanks for your help.