[AS2] Very Basic FLV Playback loading then freezing within class

[Mental]

Hi, I'm having a strange problem when I use the example from the Flash CS3 help section to simply attach and playback an FLV. For some reason, if I have the following code on the root of the swf it works fine.

var video:Video = _root["my_video"];
var netConn:NetConnection = new NetConnection();
netConn.connect(null);
		
var netStr = new NetStream(netConn);
video.attachVideo(netStr);
netStr.play("videos/video_01.flv");

However, if I have it in a class file. Then it will load the video but it will freeze on the first frame, sometimes playing a split second of sound and I can't for the life of me think why it wouldn't work.

Thanks in advance,
Mental.