2012 - I have a top down assembly and am looking at a section view (with ends capped selected) using the Front Plane.  If I select the cut surface, it shows a highlighted perimeter around the cut body.  I need to convert it to a sketch to work with and also to have the sketch update parametricly if the body changes in the feature tree above it.  How can this be done?  I have seen postings mention tools>sketch tools> intersectoin curve but this does not seem to work.  Select Entities box - as I try to select items, it highlights the exterior edges of the body beyond the section plane instead of the perimeter line generated at the section plane.  I have also tried the Create Sketch From Selections sketch command.  It requires a preselect so I preselect the face of the body at the section plane and the perimeter I want highlights.  This gives me the following error.

this has got to be one of the most basic tasks to do in solidworks so I must be doing something wrong.  I followed this exactly as stated below and got the error message shown above.  Any help would be greatly appriciated.

Create Sketch from Selections

With Create Sketch from Selections   , you can extract only those elements of a sketch (usually in an imported drawing) that you require to create a feature. You can extract a sketch, for example, and then modify it before creating a feature.

To create a sketch from selections:

1.   Edit a sketch. 

2. Select the sketch entities you want in the new sketch.

3. Click Create Sketch from Selections , or click Tools, Sketch Tools, Create Sketch from Selections.

   A new sketch appears in the FeatureManager design tree.