i cant move my main camera with the player object ?

program:-

using UnityEngine;
using System.Collections;
public class CameraTrackPlayer : MonoBehaviour {

Transform player;
float offsetx; 
// Use this for initialization
void Start () {

	GameObject player_go = GameObject.FindGameObjectWithTag("Player") ;
	if (player_go == null) {
		Debug.LogError("Coudn't found an object with tag player ");
		return;
	}
	player = player_go.transform;
	offsetx = transform.position.x - player.position.x;
}

// Update is called once per frame
void Update () {
	if (player != null) {

		Vector3 pos = transform.position;
		pos.x = player.position.x + offsetx;
		transform.position = pos;
	}
}

}

Drag the Camera onto the Player Object as a child, it should then move relative to the player.