I have read many threads with similar issues regarding "copy with mates". I am trying to copy a hex bolt, washer, lock washer and nut. When I try to select a coincident mate it says "These mate selections conflict with existing mates". If I close out of solidworks and get back in, often times it works (not always). Has this been corrected in 2017? My dialog box is pinned, so that is not the issue.