In the attached drawing when I try to extrude boss I get the error "open or overlapping figures are not supported." Normally I can zoom way in and follow the perimeter until I locate the item causing the problem. This time I can't see anything except there are three points along the centerline that are outside my figure. If I move them it distorts the figure. I can't delete them. Are they the cause of my problem? What are they and why can't I remove them?