If you have viewed the model in Shaded view, it should have Render Meshes.
Yeah, it's a little confusing, I agree. Also, the error messages need tweaking, but that's also on the TODO list.
iRhino 3D uses Render Meshes. If an object does not have a Render Mesh, iRhino 3D can't (yet) generate one. So, if you have run Shaded, you'll definitely have Render Meshes. If you have viewed the model in a Shaded view (or a Rendered view for that matter), it should have Render Meshes (unless you Save Small - which deletes Render Meshes).
Mac & windows? any viewport or perspective?
Rhino 5 for Mac or Windows. Perspective is the best bet...
unpredictable behavior could happen if you only have orthogonal viewports (I think I coded around that, but I'd need to double-check). iRhino 3D only does Perspective views and will cook up one if your file does not have one.