This time I uploaded the file rather than the editing part! It seems to run if you click on the logo rather than if you try to download (which is what I would want people to do anyway). I seem to rememeber seeing a setting somewhere to prevent downloads anyway – must see if I can find that again.
Trying it on my other machine I’ve found that sometimes it runs in Media player immediately, but other times it doesn’t. Of course everytime I try to demonstrate this it works absolutely perfectly!