How do I curve a rectangle/rectangular prism around a curved surface? I've tried everything I can think of, but something seems to go wrong every time I try something. I need this to be ready for 3D printing. Part of the model printed, but only the brim of another part printed. My professor says that something was not connected when he checked it in netfabb. Whenever I check my model with Solid Inspector2, it says there's something wrong with Nested Instances. What are those, and how do I make sure they print? I have attached pictures.

Thank you in advance,
tomed21