Hi David - you're running into some difficulty because the revolve was not quite done cleanly - it looks like the shape you revolved did not quite extend fully to the revolve axis.

Note that if you zoom in here you can see a little tiny additional additional surface:






Little tiny surface fragments like that will make for more difficulty when doing surface intersection and cutting type operations.

If you get your ellipse shape to be better constructed with the endpoints of the curve being revolved exactly aligned to the revolve axis instead of a little bit of space between the endpoints and the revolve axis you should get a better result.

- Michael