Flash in framesets plays in Mac, blacked out on PC

In an HTML frameset, I built a Flash 5 nav bar in one frame that loads a Flash 5 sub-navigation bar in a second frame, and this sub-nav bar loads HTML pages in a third frame.

I built the Flash movies on a Mac and they look and work fine on the 'net; but opening the site on my PC, I find nothing where the Flash movies sit but black rectangles.

What gives? :cyclops: