Play FLV. Why doesnt this work?

Hi,

Why doesnt the following script work to play an .flv in flashplayer 7, and why DOES it work in Flashplayer 8???

I placed an video-object on the stage with the name: my_video:

var nc:NetConnection = new NetConnection();
nc.connect(null);

var ns:NetStream = new NetStream(nc);
my_video.attachVideo(ns);

ns.play("test.flv");

I dont get it. Please help!

Grtz,
-- Barry