Thank you both for your replies. Your request to post the .3dm file of the drawing makes sense and is generous of your time.

Unfortunately, I am working with the no save trial version, so I am out of luck there.

However, If I can successfully convert this closed curve into a region and extrude it in a separate CAD program (and I can) then the drawing is 'clean', otherwise, it would not be possible to create a region.

I do not understand why I can save the CAD drawing as a region in dxf format but cannot open it in MoI. Can't MoI extrude regions brought in from a CAD drawing?

Andrew