I was following a tutorial by WalkerBoy Studios about Cameras. I have an error:

Assets/2D Mario Assets/Scripts/cameraSmoothFollow2D.js(24,61): BCE0023: No appropriate version of 'UnityEngine.Mathf.SmoothDamp' for the argument list '(float, float, UnityEngine.Vector2, float)' was found.

var cameraTarget         :    GameObject;         

var smoothTime          : float = 0.1;       
var cameraHeight         :    float = 2.5;     

var cameraFollowX      :   boolean =  true;  

var velocity          :   Vector2;

private var thisTransform           : Transform;

function Update ()
{
    if( cameraFollowX){

       thisTransform.position.x =  Mathf.SmoothDamp(thisTransform.position.x, cameraTarget.transform.position.x, velocity, smoothTime);}}

I know that the problem is the 3rd variable being a Vector 2. But in the tutorial it makes velocity a Vector 2. But how would fix this problem but have the same result as the tutorial?