Png loses transparency when published as swf

I’m working on a project where I want to use a transparent png, and when authoring in Flash CS3 (using actionscript 2.0) the png image appears transparent just as it should. However when I test it the .swf file loses the transparency entirely. The png image was saved for web from photoshop as png-24.

Anybody know why it does this, or how to fix it?

Thanks,