Hi Brian, if you hide the surface and just look at the curve and rotate around it a little bit you can see that it is kind of bent around and is not a flat planar shape.

To trim a surface with a curve like that, the curve must be planar so it knows which direction to project itself along.

The easiest way to do this is to go to the front view, select the curve, then squish it down using the edit frame, grab one of the corners and move it over until you see the "flat" snap kick in.

After I flattened the curve, then it will work to trim or boolean your surface with the curve.

- Michael