Lucky for you I DO know what the problem is. It isnt’ Windows or Mac or Linnux, or Unix or the toothfairy. It is much simpler than that. Not everyone has the latest version of Flash: Flash 8. So the earlier players still play flash movies, but not well
So you need a detection script. This will make sure that the viewer has the latest version of flash before playing the movie. If not, it will switch to another code of HTML. That code could have an image or text or even another lower grade FLA from an older version of flash.