Slenderman script problem

I am making a slenderman game in unity pro 4. Everything works fine except from 2. The follow script and the tree colliders. 1)The player won't collide with trees. Tree colliders are on. Don't know how to fix that:( 2)The script to make him follow is a bit buggy. Works good, but instead of stay, he flies in the air a meter from the ground in horizontal position. I don't know exactly where the problem is. Hope you help me:/ Here is it: #pragma strict @script RequireComponent( AudioSource )

 public var thePlayer : Transform;
 private var theEnemy : Transform;
 
 public var speed : float = 5.0;
 
 var isOffScreen : boolean = false;
 public var offscreenDotRange : float = 0.7;
 
 var isVisible : boolean = false;
 public var visibleDotRange : float = 0.8; // ** between 0.75 and 0.85 (originally 0.8172719) 
 
 var isInRange : boolean = false;
 
 public var followDistance : float = 24.0;
 public var maxVisibleDistance : float = 25.0;
 
 public var reduceDistAmt : float = 3.1;
 
 private var sqrDist : float = 0.0;
 
 public var health : float = 100.0;
 public var damage : float = 20.0;
 
 public var enemySightedSFX : AudioClip;
 
 private var hasPlayedSeenSound : boolean = false;
 
 private var colDist : float = 5.0; // raycast distance in front of enemy when checking for obstacles
 
 
 function Start() 
 {
     if ( thePlayer == null )
     {
        thePlayer = GameObject.Find( "Player" ).transform;
     }
 
     theEnemy = transform;
 }
 
 function Update() 
 {
     // Movement : check if out-of-view, then move
     CheckIfOffScreen();
 
     // if is Off Screen, move
     if ( isOffScreen )
     {
        MoveEnemy();
 
        // restore health
        RestoreHealth();
     }
     else
     {
        // check if Player is seen
        CheckIfVisible();
 
        if ( isVisible )
        {
          // deduct health
          DeductHealth();
 
          // stop moving
          StopEnemy();
 
          // play sound only when the Man is first sighted
          if ( !hasPlayedSeenSound )
          {
           audio.PlayClipAtPoint( enemySightedSFX, thePlayer.position ); 
          }
          hasPlayedSeenSound = true; // sound has now played
        }
        else
        {
          // check max range
          CheckMaxVisibleRange();
 
          // if far away then move, else stop
          if ( !isInRange )
          {
           MoveEnemy();
          }
          else
          {
           StopEnemy();
          }
 
          // reset hasPlayedSeenSound for next time isVisible first occurs
          hasPlayedSeenSound = false;
        }
     }
 
 }
 
 
 function DeductHealth() 
 {
     // deduct health
     health -= damage * Time.deltaTime;
 
     // check if no health left
     if ( health <= 0.0 )
     {
        health = 0.0;
        Debug.Log( "YOU ARE OUT OF HEALTH !" );
 
        // Restart game here!
        // Application.LoadLevel( "sceneLose" );
     }
 }
 
 
 function RestoreHealth() 
 {
     // deduct health
     health += damage * Time.deltaTime;
 
     // check if no health left
     if ( health >= 100.0 )
     {
        health = 100.0;
        //Debug.Log( "HEALTH is FULL" );
     }
 }
 
 
 function CheckIfOffScreen() 
 {
     var fwd : Vector3 = thePlayer.forward.normalized;
     var other : Vector3 = (theEnemy.position - thePlayer.position).normalized;
 
     var theProduct : float = Vector3.Dot( fwd, other );
 
     if ( theProduct < offscreenDotRange )
     {
        isOffScreen = true;
     }
     else
     {
        isOffScreen = false;
     }
 }
 
 
 function MoveEnemy() 
 {
     // Check the Follow Distance
     CheckDistance();
 
     // if not too close, move
     if ( !isInRange )
     {
        rigidbody.velocity = Vector3( 0, rigidbody.velocity.y, 0 ); // maintain gravity
 
        // --
        // Old Movement
        //transform.LookAt( thePlayer );   
        //transform.position += transform.forward * speed * Time.deltaTime;
        // --
 
        // New Movement - with obstacle avoidance
        var dir : Vector3 = ( thePlayer.position - theEnemy.position ).normalized;
        var hit : RaycastHit;
 
        if ( Physics.Raycast( theEnemy.position, theEnemy.forward, hit, colDist ) )
        {
          //Debug.Log( " obstacle ray hit " + hit.collider.gameObject.name );
          if ( hit.collider.gameObject.name != "Player" && hit.collider.gameObject.name != "Terrain" )
          {         
           dir += hit.normal * 20;
          }
        }
 
        var rot : Quaternion = Quaternion.LookRotation( dir );
 
        theEnemy.rotation = Quaternion.Slerp( theEnemy.rotation, rot, Time.deltaTime );
        theEnemy.position += theEnemy.forward * speed * Time.deltaTime;
 
        // --
     }
     else
     {
        StopEnemy();
     }
 }
 
 
 function StopEnemy() 
 {
     transform.LookAt( thePlayer );
 
     rigidbody.velocity = Vector3.zero;
 }
 
 
 function CheckIfVisible() 
 {
     var fwd : Vector3 = thePlayer.forward.normalized;
     var other : Vector3 = ( theEnemy.position - thePlayer.position ).normalized;
 
     var theProduct : float = Vector3.Dot( fwd, other );
 
     if ( theProduct > visibleDotRange )
     {
        // Check the Max Distance
        CheckMaxVisibleRange();
 
        if ( isInRange )
        {
          // Linecast to check for occlusion
          var hit : RaycastHit;
 
          if ( Physics.Linecast( theEnemy.position + (Vector3.up * 1.75) + theEnemy.forward, thePlayer.position, hit ) )
          {
           Debug.Log( "Enemy sees " + hit.collider.gameObject.name );
 
           if ( hit.collider.gameObject.name == "Player" )
           {
               isVisible = true;
           }
          }
        }
        else
        {
          isVisible = false;
        }
     }
     else
     {
        isVisible = false;
     }
 }
 
 
 function CheckDistance() 
 {
     var sqrDist : float = (theEnemy.position - thePlayer.position).sqrMagnitude;
     var sqrFollowDist : float = followDistance * followDistance;
 
     if ( sqrDist < sqrFollowDist )
     {
        isInRange = true;
     }
     else
     {
        isInRange = false;
     }  
 }
 
 
 function ReduceDistance() 
 {
     followDistance -= reduceDistAmt;
 }
 
 
 function CheckMaxVisibleRange() 
 {
     var sqrDist : float = (theEnemy.position - thePlayer.position).sqrMagnitude;
     var sqrMaxDist : float = maxVisibleDistance * maxVisibleDistance;
 
     if ( sqrDist < sqrMaxDist )
     {
        isInRange = true;
     }
     else
     {
        isInRange = false;
     }  
 }
 
 
 function OnGUI()
 {
     GUI.Box( Rect( (Screen.width * 0.5) - 60, Screen.height - 35, 120, 25 ), "Health : " + parseInt( health ).ToString() );
 }