CS4 not exporting PNG correctly

I'm a new user to CS4, and when I try to export a flash file with alpha/transparent values to PNG, the transparent qualities don't transfer over to the PNG.
For example this image would have a solid black background instead of a transparent one.

Previously in Flash8, this process worked perfectly.

Is there something I need to enable in CS4 in order to preserve alpha values? :/

My export settings/method:
file>export image>png>saveaspng>seescreenshot
Attachment 74325

Thanks. :)