Without seeing the .S01 file it's impossible to tell what the issue might be. Note that DWG does not necessarily support all of the things that Stardraw can do, so you may have an object in your Stardraw file that AutoCAD can't handle - this could explain the error.
Can you zip up the .S01 file and attach it to a post to this forum? We'd be happy to take a look and see what's going on. Kind regards,Rob RobinsonStardraw.com