Why is NetStream FLV playback interrupted when using the preloader?

I have an FLV that I would like to play. The following code works fine when launching SWF directly:

    var sUrl:String = m_pMovieUrlList[iMovieIndex];
    m_kNetConnection = new NetConnection();
    m_kNetConnection.connect(null);
    m_kNetStream = new NetStream(m_kNetConnection);
    m_kNetStream.client = this;
    m_kVideo = new Video();
    m_kVideo.attachNetStream(m_kNetStream);
    m_kMovieContainer.addChild(m_kVideo);
    m_kNetStream.play(sUrl);

      

        
        
        
      

    

However, when it runs inside the preloader, I get a NetStream.Play.StreamNotFound NetStatusEvent. Why is this happening and how can I get it to work?