OK I'm using SW2011 x64 (SP5.0) and I have a huge assembly which is entirely driven by a master sketch model. All parts in my assembly are created using the master model (i.e. top-down modeling technique where the first feature in every part is to insert the master sketch model and then use it to define geometry, interfaces, etc). This technique is awesome but I have one major problem. I'm using some blocks in my master sketch model showing some mated connectors. In my assemblies, when I define the connector positions and constrain them to lines on the sketch blocks (which locates them per the master model), every time I regenerate the assembly the mate constraints completely make up new relations and all my connectors end up in the wrong place. What seems to be happening is that every time I regenerate & save my master model, the internal ID of lines within the sketch blocks seem to be changing and so in the assembly, the connector mate constraints end up wherever the internal ID of the sketch block line moved to. This is maddening and makes using blocks completely worthless. I've seen others have issues with this and have read all the threads. Many simply say to not "link" the sketch block. Mine aren't linked....so this isn't the problem. Does anyone have any ideas how to prevent this from happening? I have fixed the constraints about 10 times now and it just keeps happening. Please reply if you have any suggestions.