Trim Surface

You can use a surface, plane, or sketch as a trim tool to trim intersecting surfaces. You can also use a surface in conjunction with additional surfaces, as mutual trim tools. Trim surface includes the following options:

To trim a surface:

1. Create two or more surfaces that intersect at one or more points, or create a surface that intersects with a plane or has a sketch on its face. 
2. Click Trim Surface on the Surfaces toolbar, or click Insert > Surface > Trim. 
3. In the PropertyManager, under Trim Type, select a type: 
   • Standard. Trims surfaces using surfaces, sketch entities, curves, planes, and so on. 
   • Mutual. Trims multiples surfaces using the surfaces themselves.
4. Under Selections, choose from these options: 
   • Trim tool (available with Standard selected under Trim Type). Select a surface, sketch entity, curve, or plane in the graphics area as the tool that trims other surfaces. 
   • Surfaces (available with Mutual selected under Trim Type). Select multiple surfaces in the graphics area for Trimming Surfaces to use to trim themselves. 
   • Select a trim action: 
     • Keep selections. Retains the surfaces listed under Pieces to Keep . Intersecting surfaces not listed under Pieces to Keep are discarded. 
     • Remove selections. Discard the surfaces listed under Pieces to Remove . Intersecting surfaces not listed under Pieces to Remove are retained.
      
   • Select surfaces in Pieces to Keep or in Pieces to Remove , based on the trim action.
5. Under Surface Split Options, select an item: 
   • Natural. Forces the boundary edges to follow the shape of the surface. 
   • Linear. Forces the boundary edges to follow a linear direction from the trim point. 
   • Split all. Display all splits in the surface. 
6. Click

Example Using Standard Trim Type
Sketch used for Trim tool	Pieces to Keep with Natural selected in Surface Split Options	Trimmed surface
Example Using Mutual Trim Type
Two intersecting surfaces	Surfaces selected for Pieces to Keep	Trimmed surface

I've been trying to trim surfaces using the steps above.  They do not work!!!  I keep getting an error that asks for a surface to trim.  It is set om "mutual" so the surfaces are supposed to trim each other.  THEY DON"T!!  How do I get this to work???