When a pack and go collects the files for shipment I sometimes get a part which is dependent upon a part/assembly which cannot be found. I am assuming that this part has an external reference to the part or assembly. However the part itself seems fine and resolves ok. How can I find the problem? All sketches seem to look OK. No warnings, errors, or flags that I can see. How can I determine the original reference connection so that I can fix or break it?