How do I save a drawing file (vb.net)

Can anyone help me out.  I am pulling my hair out and getting bald pretty quickly here.

All I want to do is save an open slddrw file to a specified location.  I have found code to save in all the different formats except drawing.

This is what I have currently, and it errors out at runtime with a type mismatch error:

Public swDraw As DrawingDoc

...

swDraw.Extension.SaveAs(swModel.GetPathName & ".DWG", _

            swSaveAsVersion_e.swSaveAsCurrentVersion, swSaveAsOptions_e.swSaveAsOptions_Silent, Nothing, errors, warnings)

SolidworksApi macros