Photoview360 render region not shown

When I choose "Render Region" from the Photoview360 menu, the region normally appears in pink and I can adjust it.

However, for some reason, it has totally disappeared and I can't find a way of getting it back. When I DO enable it, and
do a render, I just get a black screen.

Is there any way of resetting the render region?

Thanks!

SolidworksPhotoview 360