When I try something like this:
Actionscript Code:
function videoLoad(n:Number):void
{
    activeClip=n-1;
    var nsString:String = ("assets/video/question"+n+".flv");
    var video:Video = new Video();
    var conn:NetConnection = new NetConnection();
    conn.connect(null);
    var stream:NetStream = new NetStream(conn);
    video.attachNetStream(stream);
    var material:VideoStreamMaterial = new VideoStreamMaterial (video, stream);
    material.animated = true;
    stream.play(nsString);
    gridBoxArray[activeClip].replaceMaterialByName(material, "back")


I get the following error:
SecurityError: Error #2123: Security sandbox violation: BitmapData.draw: file:///MacintoshHD/Users/pajhonka/Sites/main/about.swf cannot access null. No policy files granted access.
at flash.display::BitmapData/draw()
at org.papervision3d.materials::MovieMaterial/drawBitmap()
at org.papervision3d.materials::MovieMaterial/createBitmapFromSprite()
at org.papervision3d.materials::MovieMaterial/set texture()
at org.papervision3d.materials::MovieMaterial()
at org.papervision3d.materials::VideoStreamMaterial()
at about_fla::MainTimeline/videoLoad()
at Function/http://adobe.com/AS3/2006/builtin::apply()
at com.greensock.core::TweenCore/complete()
at com.greensock::TweenLite/renderTime()
at com.greensock.core::SimpleTimeline/renderTime()
at com.greensock::TweenLite$/updateAll()