Playing sound on an Instantiated Prefab

Hello everyone. I'm fairly new to Unity but pretty advanced in other scripts such as JS and AS. So I have a prefab with this script attached:

 #pragma strict

 var prospectTime : int;
 var prospectAudio : AudioClip;
 private var time : float = 0.0f;

 function OnMouseDown () {
     if (Vector3.Distance(transform.position, GameObject.FindGameObjectWithTag("Player").transform.position) < 6)
         time = 0.1f;
 }

 function Update () {
     if (time > 0) {
         time += 1 * Time.deltaTime;
     }
     if (time > prospectTime) {
         activate();
     }
 }

 function activate () {
     var zone : Zone = transform.parent.transform.parent.transform.parent.GetComponent(Zone);
     var a = transform.parent.transform.parent.name.Split(":"[0]);
     if (zone.activateData(transform.parent.name, int.Parse(a[1]), int.Parse(a[2])) == true) {
         AudioSource.PlayClipAtPoint (prospectAudio, transform.position);    
         transform.parent.active = false;
     }
     time = 0.0f;
 }

 function OnMouseUp () {
     time = 0.0f;
 }

This works, however if i try to play the sound with

 audio.Play(prospectAudio);

it will throw an error:

BCE0023: No appropriate version of 'UnityEngine.AudioSource.Play' for the argument list '(UnityEngine.AudioClip)' was found.

 audio.PlayOneShot(prospectAudio);

also throws an error:

MissingComponentException: There is no 'AudioSource' attached to the "Coal1" game object, but a script is trying to access it.

In inspector I did drag the audio on the script's prospectAudio variable.

What's wrong? I would like to use the audio.Play and audio.PlayOneShot but it seams I can't :)

Can someone explain please?