I was finding it difficult to adjust the distance of the dimension lines from the drawn line in a file originally created in AutoCad. After much trial and error, I found the secret was to be sure there was a setting greater than 0" for the "Size" setting in "Arrows". From the main window, select Format>Dimension Style>Arrows. Input a value greater than 0" (I used 4"). This apparently keeps 2 control points from sitting atop one another and makes it possible to slide the dimension line further from of closer to the line being measured.

Hope this saves someone the hour it took me to figure this out!