Interestingly I solved the problem myself, by accident
I transferred the file I was working on to my laptop. played the presentation as was willing to live the the problem for the next while until solved, however it worked fine without the annoying prompting question about potential virus threats.
Solution? I forgot that on my laptop I use Windows Media Classic Player, which has eliminated the problem whereas on my desktop I have been using Windows Media Player since I reinstalled Win 7 and haven't bothered to reinstall Classic, which I used to use most often.
Anyway, short answer....use Windows Media Classic Player.
Still ..........it would be nice to know how to eliminate the problem when using Windows Media Player.
BTW, never at any stage was I not 'calm', just providing detailed information to eliminate superfluous answers or at least give those trying to help an idea of what I have already tried.
In any event, I think this is a great site and have found many ideas from reading the forum and articles.