You might be selecting the interpret instead of convert on the units. My guess is the parts are becoming so small that you cannot see them. When changing units you want to convert where 1" becomes 25.4 mm instead of 1" becomes 1 mm; this is scaling. Again this is my guess on the files disappearing and also check to see if you have a filter on your simplified reps that hide anything a certain size. You can set a size on the find command that will change the status of certain size parts; great to filter out fasteners on huge equipment. Eric