I am trying to create a chamfer dimension on a drawing. I created the chamfer in my part. When I try to create the chamfer dimension, I select the chamfer edge, I select a straight edge (I've tried both the horizontal and verical edges near my chamfer) and I get the error "Cannot create chamfer with the selected edge. Please select another edge." All the edges have been rounded. Is that my problem? The chamfer in question is the one in the lower left corner in the image below. Thanks for your help.

Carrie