I get this error message when trying to set a coincident relation between the midpoints of two perpendicular lines (by right-clicking on one of the lines and choosing Select Midpoint from the drop-down, then holding down Ctrl and repeating with the other line). I even tried placing a sketch point on the midpoint of one of the lines and using that along with right-clicking on the other line and choosing Select Midpoint from the drop-down. Same message. I could then click on this sketch point and drag it. It would snap to the midpoint of the other line just fine, and set the relation. I don't remember this happening on previous versions, but I'm not sure it's new.
Of course I can get it to work by placing the sketch point and dragging it to the other line, but I'm curious why one method works and the other doesn't. Any ideas, or is anyone else seeing this?