AI bug issue

Below is a semi intelligent ai script. It works, but it has an issue with the rotation. Locking the rigidbody's rotation x and z. (None of the units are meant to move up and down, as the entire game is set on a flat surface.) Anyway, the ai basically does a barrel roll and prevents the computer to from actually moving around an object.

In addition, locking the y position on the rigidbody for some reason also causes the ai to only look at the target, instead of following the target. The only other codes attached are a instantiating code to fire a projectile, and a code to animate the simple gun to fire.

The code is below, and any thoughts are appreciated.

     #pragma strict
     @script RequireComponent (Rigidbody)
     
     private var myTransform : Transform; 
     private var myRigidbody : Rigidbody;
     
     var target : Transform; // the player
     var movespeed : float = 6.0;
     var turnspeed : float = 1.0;
     var rayDistance : float = 10;
     var mp : float = .35;
     
     
     private var desiredVelocity : Vector3;
     var isGrounded : boolean = false;
     
     function Start () 
     {
         myTransform = transform;
         myRigidbody = rigidbody;
         
         myRigidbody.freezeRotation = true;
     }
     
     function Update () 
     {
         Moving();
         
     }
     
     function Moving()
     {
         //rotation
         var lookDirection : Vector3 = (target.position - myTransform.position).normalized;
         
         var hit : RaycastHit;
         
         var shoulderMultiplier : float = mp;
         
         var leftRayPos : Vector3 = myTransform.position - (myTransform.right * shoulderMultiplier);
         var rightRayPos : Vector3 = myTransform.position + (myTransform.right * shoulderMultiplier);
     
     
         if (Physics.Raycast (leftRayPos, myTransform.forward, hit, rayDistance))
         {
                 Debug.DrawLine (leftRayPos, hit.point, Color.red);
                 lookDirection += hit.normal * 1.0;
         }
         else if (Physics.Raycast (rightRayPos, myTransform.forward, hit, rayDistance))
         {
                 Debug.DrawLine(rightRayPos, hit.point, Color.red);
                 lookDirection += hit.normal * 1.0;
         }
         else
         {
             Debug.DrawRay(leftRayPos, myTransform.forward * rayDistance, Color.yellow);
             Debug.DrawRay(rightRayPos, myTransform.forward * rayDistance, Color.yellow);
     
         }
         
         var lookRot : Quaternion = Quaternion.LookRotation( lookDirection );
     
                 
         myTransform.rotation = Quaternion.Slerp (myTransform.rotation, lookRot, turnspeed * Time.deltaTime);
     
         //movement
         desiredVelocity = myTransform.forward * movespeed;
         desiredVelocity.y = myRigidbody.velocity.y;
     }
     
     function FixedUpdate()
     {
         if(isGrounded)
         {
         myRigidbody.velocity = desiredVelocity;
         }
     }
     
     
     function OnCollisionEnter (collision : Collision)
         {
             if ( collision.collider.gameObject.name == "Floor")
                 {
                     isGrounded = true;
                 }
         }
     function OnCollisionStay (collision : Collision)
         {
             if ( collision.collider.gameObject.name == "Floor")
                 {
                     isGrounded = true;
                 }
         }
     function OnCollisionExit (collision : Collision)
         {
             if ( collision.collider.gameObject.name == "Floor")
                 {
                     isGrounded = false;
                 }
         }