Can't ios load a scene file? Bug?

I pack a scene to xx.unity3d file and upload to server. But I meet a error when load and init xx.unity3d file in ios. why?
no problem in editor!

error:

my code:

IEnumerator Start () {

WWW download = WWW.LoadFromCacheOrDownload (“http://xxxxxxxxxxx/scenefile_iPhone.unity3d”, 1);
yield return download;

if (download.error != null)
{
Debug.LogError(download.error);
return false;
}

AssetBundle bundle = download.assetBundle;

Application.LoadLevelAsync(“BruceModel”);

}

anyone have a same problem?