Here I'm trying to replicate the bisected red square that you see going off the screen in the upper left. I have a red rounded square underneath a white shape and I'm trying to use the CUT PATH function. Inkscape rejects the operation, claiming that one of the objects is not a path but they quite blatantly are both paths, as can be seen from those grey node things.

it would be easier to help if you posted a file, but at a guess the red rounded rectangle needs to be converted to a path (object to path command) before engaging in Boolean heroics.

Thanks; you're right. For soem reason it was resistant to becoming a path. I don't understand why it took multiple attempts to turn it into a path.