Unexpected token: targetPos

Try :

 function CalculateAimPosition (targetPos:Transform)
 {
     var aimPoint = Vector3(targetPos.x + aimError, targetPos.y + aimError, targetPos.z + aimError);
  
     desiredRotation = Quaternion.LookRotation(aimPoint);
 }

EDIT : here is the entire script :

 var myProjectile : GameObject;
 var reloadTime : float = 1f;
 var turnSpeed : float = 5f;
 var firePauseTime : float = .25f;
 var muzzleEffect : GameObject;
 var errorAmount : float = 0.01f;
 var myTarget : Transform;
 var turretBall: Transform;
 var muzzlePositions : Transform;
 var targetPos : Transform;
 
 private var nextFireTime : float;
 private var nextMoveTime : float;
 private var desiredRotation : Quaternion;
 private var aimError : float;
 
 function Start () {
 
 }
 
 function Update () {
 
     if(myTarget)
     {
         if(Time.time >= nextMoveTime)
         {
             CalculateAimPosition(myTarget.position);
             turretBall.rotation = Quaternion.Lerp(turretBall.rotation.desiredRotation.time.deltaTime * turnSpeed);
         }
         if(Time.time >= nextFireTime)
         {
             FireProjectile();
         }
     }
 }
 
 function OnTriggerEnter (other : Collider) {
     if (other.gameObject.tag == "Enemy")
     {
         nextFireTime = Time.time + (reloadTime * 0.5);
         myTarget = other.gameObject.transform;
     }
 }
 
 function OnTriggerExit (other : Collider){
     if(other.gameObject.transform == myTarget)
     {
         myTarget = null;
     }
 }
 
 function CalculateAimPosition (targetPos : Vector3) {
     var aimPoint = Vector3(targetPos.x + aimError, targetPos.y + aimError, targetPos.z + aimError);
     desiredRotation = Quaternion.LookRotation(aimPoint);
 }
 
 function CalculateAimError {
     aimError = Random.Range(-errorAmount, errorAmount);
 }
 
 function FireProjectile {
     audio.Play();
     nextFireTime = Time.time + reloadTime;
     nextMoveTime = Time.time + firePauseTime;
     CalculateAimError();
 
     for(theMuzzlePos in muzzlePositions)
     {
         Instantiate(myProjectile, theMuzzlePos.position, theMuzzlePos.rotation);
         Instantiate(muzzleEffect, theMuzzlePos.position, theMuzzlePos.rotation);
     }
 }