Why is my enemy not doing his run animation?

Ok so I’m new to Unity and Scripting. I found this script in a website and I tweeked it a little bit so that my enemy can idle when it’s out of range and Run when it’s in range and attack when it’s in range. so far my enemy idle when out of range but it doesn’t do the Run animation when it’s following the player. Can someone Rely this with my code fixed? so that it can attack in Range, Run in range and Idle out of range from player? my enemy only has idle, Start (start runing), Run, End (end Running) and Attack.

here is the code i need fixed:

var moveSpeed = 3; //move speed
var rotationSpeed = 3; //speed of turning
var attackThreshold = 3; // distance within which to attack
var chaseThreshold = 10; // distance within which to start chasing
var giveUpThreshold = 10; // distance beyond which AI gives up
var attackRepeatTime = 1; // delay between attacks when within range

private var target : Transform; //the enemy’s target
private var initialSpeed = 0;
private var chasing = false;
private var attackTime = 1;

var myTransform : Transform; //current transform data of this enemy

function Awake()
{
myTransform = transform; //cache transform data for easy access/preformance
}

function Start()
{

 target = GameObject.FindWithTag("Player").transform; //target the player
  if (!target)
  Debug.Log ("ERROR : player not tagged as 'Player'");

// Set all animations to loop
animation.wrapMode = WrapMode.Loop;

// Except our action animations, Dont loop those
animation["End"].wrapMode = WrapMode.Once; 
animation["idle"].wrapMode = WrapMode.Once;
animation["Start"].wrapMode = WrapMode.Once;

	
// Put idle and run in a lower layer. They will only animate if our action animations are not playing
animation["idle"].layer = 1;
animation["Attack"].layer = 1;

animation.Stop();

}

function Update () {

Debug.DrawLine( target.position , myTransform.position , Color.cyan);

// check distance to target every frame:
var distance = (target.position - myTransform.position).magnitude;

if (chasing) { 


    //rotate to look at the player
    myTransform.rotation = Quaternion.Slerp(myTransform.rotation,
    Quaternion.LookRotation(target.position - myTransform.position), rotationSpeed*Time.smoothDeltaTime);
  
    

    //move towards the player
    myTransform.position += myTransform.forward * moveSpeed * Time.smoothDeltaTime; 
    animation["Run"].layer = 1;

    // give up, if too far away from target:
    if (distance > giveUpThreshold) {
        chasing = false;
        animation["idle"].layer = 1;
        
        
    }

    // attack, if close enough, and if time is OK:
    if (distance < attackThreshold && attackTime == attackRepeatTime) {
        // Attack! (call whatever attack function you like here)
        attackTime = attackTime + attackRepeatTime;
        // Attack Animation
        //animation.CrossFade("attack_animation");
        //animation.Play();
    }

} else {
    // not currently chasing.

    // start chasing if target comes close enough
    if (distance < chaseThreshold) {
        chasing = true;
        animation["Run"].layer = 1;
      
    }
	if (chasing == true ){
							animation.CrossFade("Run");
							animation.Play();

							
						}
			else if (chasing == false)
										{
										animation.CrossFade("Start");
										animation.Play();
										}

}

}

found one script that finally works!!!
using UnityEngine;
using System.Collections;

public class EnemyBehavior : MonoBehaviour
{
public enum EnemyState{IDLE = 0, WALK = 1, RUN = 2, ATTACK = 3, KILL = 4};
public AnimationClip enemyIdle;//setting animations
public AnimationClip enemyWalk;//walking
public AnimationClip enemyRun;//running/chasing
public AnimationClip enemyAttack;//attacking player
public AnimationClip enemyKill;//killing player

 public Transform Player;//adds the player to the script

 private int Stopped = 0;
 public int WalkingSpeed = 1;//sets the normal walking speed
 public int RunningSpeed = 5;//sets the running (chase player) speed
 public int DefaultRunningSpeed = 5;
 public int MaxDist= 8;//maximum distance the player can be before enemy stops chasing the player
 public int MinDist= 1;//how close the player can be to enemy for enemy to start chasing player
 public EnemyState currentState;

 private bool PlayerDetected;

 void Update()
 {
    if(Vector3.Distance(transform.position,Player.position) <= MaxDist)//if that object has the tag "Player"
    {
      PlayerDetected = true;
      if (PlayerDetected)
      {
       print ("Player Detected.");
       transform.LookAt(Player);//Looks at the player
       currentState = EnemyState.RUN;
         transform.position += transform.forward*RunningSpeed*Time.deltaTime;//follows the player
      }
    }else if(Vector3.Distance(transform.position,Player.position) > MaxDist)
    {
      RoamAround ();
    }
    if (Vector3.Distance (transform.position,Player.position) < MinDist)
    {
      currentState = EnemyState.ATTACK;
      Attack ();

    }

    if (currentState == EnemyState.IDLE)
    {
      //print ("The enemy is idle.");
      animation.CrossFade (enemyIdle.name);
    }
    else if (currentState == EnemyState.WALK)
    {
      print ("The enemy is walking.");
      animation.CrossFade (enemyWalk.name);
    }
    else if (currentState == EnemyState.RUN)
    {
      print ("The enemy is running.");
      print ("Distance: " + Vector3.Distance(transform.position,Player.position));
      animation.CrossFade (enemyRun.name);
      RunningSpeed = DefaultRunningSpeed;
    }
    else if (currentState == EnemyState.ATTACK)
    {
      print ("The enemy is attacking.");
      animation.CrossFade (enemyAttack.name);
      RunningSpeed = Stopped;
    }
    else if (currentState == EnemyState.KILL)
    {;
      print ("The enemy is killing.");
      animation.CrossFade (enemyKill.name);
    }

 }
 void RoamAround()
 {
    currentState = EnemyState.IDLE;//Add other RoamAround stuff here
 }
 public void Attack()
 {
    //Add attacking stuff here
    //Application.LoadLevel ("GameOver");
 }

}