Third Person Cam Not Working

using UnityEngine;
using System.Collections;

public class ThirdPersonCamera : MonoBehaviour
	public float smooth = 3f;		// a public variable to adjust smoothing of camera motion
	Transform standardPos;			// the usual position for the camera, specified by a transform in the game
	Transform lookAtPos;			// the position to move the camera to when using head look
	void Start()
		// initialising references
		standardPos = GameObject.Find ("CamPos").transform;
		if(GameObject.Find ("LookAtPos"))
			lookAtPos = GameObject.Find ("LookAtPos").transform;
	void FixedUpdate ()
		// if we hold Alt
		if(Input.GetButton("Fire2") && lookAtPos)
			// lerp the camera position to the look at position, and lerp its forward direction to match 
			transform.position = Vector3.Lerp(transform.position, lookAtPos.position, Time.deltaTime * smooth);
			transform.forward = Vector3.Lerp(transform.forward, lookAtPos.forward, Time.deltaTime * smooth);
			// return the camera to standard position and direction
			transform.position = Vector3.Lerp(transform.position, standardPos.position, Time.deltaTime * smooth);	
			transform.forward = Vector3.Lerp(transform.forward, standardPos.forward, Time.deltaTime * smooth);
says The namespace `global::' already contains a definition for `ThirdPersonCamera'

try to use the default camera of the standard assets