I've run into this a time or two before, and it happened again today, so I thought I'd ask and see if anyone knows what's going on.  I tried to drag this bolt into an Assembly and it wouldn't snap into place.  I opened it, and the "Mate References" folder and its contents are grayed out.  It looks like it's suppressed, but I know I didn't do it, and no one else here would have, and I can't figure out a way to un-suppress it.  I can choose "Edit definition" from the right-click drop-down, but when I exit the edit function it goes right back to grayed out.  Does anyone have any ideas?  I know I can delete it and create a new one, but I'd like to fix it if possible, and so I'll know for the future.