Sound problem

Hello, I use QCAR-iOS-1.0.0beta1.unitypackage, my MacOS version is 10.6.7 Xcode version Version 4.1 (4B110f), Unity version is 3.4.0 f5, my iPhone device model is iPhone 4 GSM, OS vision 4.3.2 the problem is, there is no sound when I run the application on my iPhone , I didn't face this problem with android . I have an audio clip (mp3 format) and I attached to my ImageTarget object in Unity , I want to play this clip when ImageTarget is detected and pause it when the target lost , so I modified the code in TrackableEventHandler.cs as the following : private void OnTrackingFound() { Renderer[] rendererComponents = GetComponentsInChildren(); // Enable rendering: foreach (Renderer component in rendererComponents) { component.enabled = true; } audio.Play(); Debug.Log("Trackable " + mTrackableBehaviour.TrackableName + " found"); } private void OnTrackingLost() { Renderer[] rendererComponents = GetComponentsInChildren(); // Disable rendering: foreach (Renderer component in rendererComponents) { component.enabled = false; } audio.Pause(); Debug.Log("Trackable " + mTrackableBehaviour.TrackableName + " lost"); } ------------ as you see audio.Play() & audio.Pause() has been added. and the audio clip is already attached to my ImageTaregt object in Unity, but there is no sound . my clip is 2D sound and I checked all its attributes including the volume. please how to solve this problem. Thank you,,,