NavMashAgent not moving in Unity3D 5

Here is my code. Im trying to move a Cube to CheckPoints. FindClosestTarget() method collect all Checkpoints. When Cube hit the CheckPoint, ChackPoint will be Set as Inactive. When the Collision happens FindClosestTarget() call again and get the new closest CheckPoint. Thing is Cube not moving. It Look at the closest check point but not moving. I'm I doing something wrong here?

 using UnityEngine;
 using System.Collections;
 
 public class EnimyAI03N : MonoBehaviour {
 
     NavMeshAgent agent;
     Transform Target;
     private float rotationSpeed=15.0f;
 
     void Start () {
         agent = GetComponent<NavMeshAgent>();
         Target = FindClosestTarget ().transform;
     }
 
     void Update () 
     {
         LookAt (Target);
         MoveTo (Target);
 
     }
 
     // Turn to face the player.
     void  LookAt (Transform T){
         // Rotate to look at player.
         Quaternion rotation= Quaternion.LookRotation(T.position - transform.position);
 
         transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.deltaTime*rotationSpeed);
         //transform.LookAt(Target); alternate way to track player replaces both lines above.
 
     }
 
     void  MoveTo (Transform T){
         agent.SetDestination(T.position); 
     }
 
     void OnCollisionEnter (Collision col)
     {
 
         if(col.gameObject.name.Contains("CheckPoint"))
         {
             Target = FindClosestTarget ().transform;
         }
     }
 
     GameObject FindClosestTarget() {
         GameObject[] gos;
         gos = GameObject.FindGameObjectsWithTag("CheckPoint");
 
         GameObject closest=null;
         float distance = Mathf.Infinity;
         Vector3 position = transform.position;
         foreach (GameObject go in gos) {
             Vector3 diff = go.transform.position - position;
             float curDistance = diff.sqrMagnitude;
 
             if (curDistance < distance) {
                 closest = go;
                 distance = curDistance;
             }
         }
         return closest;
     }
 
 }