We need more information to make any useful suggestions. A screen shot or two would help to show what you have.
My only guess would be that the surface may not fully intersect the part or has a hole.
Not enough information provided for a meaningful response. Provided additional details about the geometry and ideally post the model. If you can not post the model then add enough pictures of the geometry and model tree to describe the issue.
In Creo if you want to cut to a surface, the surface that you're cutting to needs to extend past the geometry that you're cutting. There are a bunch of ways to accomplish this. I prefer to use the extend command in data doctor to ensure that my surface extends past my geometry.
See the examples below: