Flash player can only play .swf files. It can't play video formats of any kind (including .flvs). To play an .flv you need either an external player like VLC Media Player or the one you have, or, you can import the .flv into flash, load it into an flvplayback component (this is all done when you go through the File > Import > Import Video... wizard) and then export it as an .swf
General notice: from now on, I would like to ask everyone to put [AS2] or [AS3] (corresponding to the version of actionscript you are using on your project) in front of their post titles when the question is actionscript related! Please help us help you faster. Thank you.