I have a Plane that has been rotated and extruded into a "Square" shape, that I am trying to take an ovular chunk out of with a deformed Cylinder. I have had a multitude of problem with this and have spent the last several hours trying to work out why it won't work. As you can see in the image: It shows me where it should cut, but doesn't cut it. The Edges it has made inside the shape aren't attached to a Vertex and they are intangible. The other problem is obviously the shape hasnt been cut so the faces / edges / vertex are still on the side. I honestly have no clue what to do. and because of this I cant even begin to fix them for the Subsurf mod.