A single figure will cast shadows on that conglomerate prop I described, but not the collection of 5 that I need for several scenes.  That suggests memory problems. I've reduced bucket size and raised shading rate, to no avail.

I confess I'm clueless about diffuse components, but I went to the advnaced panel of the material window for that prop and took the attached screen shot in the hope you can perhaps interpret it.

Is there any way to change those values to something more likely to show a shadow?