Unity audioclip load errror on WP8 and not on Android - windows-phone-8

Question

I developed a game using Unity 2d for Android and WP8. The games is about a player that goes through a level eating orange. When the player collides with an orange it plays a soundclip.
So, when you play the first time, there is no matter, all sounds play well. Then when you choose go to menu option to start again the level, the game crashes at the first collide. If then you chose menu, and reload the level, it works fine.
So it works well once , then fails once, then works well once, and go on the same.
This erros happens in WP8 and not in Android.
The problem is in WP8 with this code:
void OnTriggerEnter2D(Collider2D collider){
if (collider.tag == "Player") {
NotificationCenter.DefaultCenter ().PostNotification (this, "IncrementarPuntos", this.puntosGanados);
AudioSource.PlayClipAtPoint (itemSoundClip, Camera.main.transform.position, itemSoundVolume);
Destroy (this.gameObject);
}
}
the line with error is
AudioSource.PlayClipAtPoint (itemSoundClip, Camera.main.transform.position, itemSoundVolume);
because itemSoundClip is null.
I dont understand why itemSoundClip sometimes goes null.
this is the exception
$exception {System.NullReferenceException: Object reference not set to an instance of an object.
at UnityEngine.AudioSource.PlayClipAtPoint(AudioClip clip, Vector3 position, Single volume)
at Item.OnTriggerEnter2D(Collider2D collider)
at Item.$Invoke0(Int64 instance, Int64* args)
at UnityEngine.Internal.$MethodUtility.InvokeMethod(Int64 instance, Int64* args, IntPtr method)} System.Exception {System.NullReferenceException}
Something important to know.
My orange item is a prefab. This item have a script which I add a clip sound(itemSoundClip)
In my scene I use a Generator script which takes that orange item, and creates instances of it in a random time with this line
Instantiate (obj [Random.Range (0, obj.Length)], transform.position, Quaternion.identity);
Maybe when Instantiates ocurrs, the item cant load the clip?

Answer 1

In my unity project, i play sound in WP8:
public AudioClip coinCollect;
void OnTriggerEnter(Collider other)
{
if (other.gameObject.name == "coin_gold")
{
AudioSource.PlayClipAtPoint(coinCollect, other.gameObject.transform.position,1);
gold++;
Destroy(other.gameObject);
}
}
And in Unity Inspector i add my sound

Answer 2

I find a solution. If the variable of itemClipSound is null, then I load the sound through Resources with this.
if (itemSoundClip == null)
itemSoundClip = (AudioClip) Resources.Load("cogerItem");