Quaternion.Slerp not working

Hi guys, In a game set in space I'm working on, I can't seem to get an object to face the camera, as well as end up level to the camera, using LookRotation(). I believe it's because the camera could be at any arbitrary angle. I have been able to get the rotation to work on two axis, x & y, but the object is not rotated correctly on the z axis so it's not level with respect to the camera.

Setup: An object is parented to an empty GameObject which in turn is parented to my camera. The empty GameObject is 15 units down the Z-axis, and the object is parented to the empty GameObject's origin.

The camera flies around space before stopping, and the object appears in front of the camera rotating using a rigid body . So when the tractor beam is activated by the user, the position / rotation of the camera is arbitrary and the Slerp rotates the object. The script below works fine until the camera is rotated.

using UnityEngine; using System.Collections;

public class test_rotate : MonoBehaviour {

 public Transform target;
 Vector3 targetV3;   // Vector3 of camera (for LookRotation)
 Quaternion rotateTo; //used to store LookAt angle
 bool beamOn; 
 public Rigidbody rb;
 int counter = 0; //counter for frames 
 float tracterBeamSpeed = 5f; //modifies the speed of rotating the object to face camera

 void Start () {
     rb.AddRelativeTorque (new Vector3 (50f, 500f, 150f));  //sets the object rotating
 }

 void Update () {
     if (beamOn) 
     {
         counter++;
         if (counter <= 40) {
         transform.rotation = Quaternion.Slerp (transform.rotation, rotateTo, Time.deltaTime * tracterBeamSpeed);
         Debug.Log("rotating" +counter);
         } else {
             beamOn = false;
             counter = 0;
             Debug.Log("done rotating");
         }
     }
 }
 //button triggers this method
 public void RotateStart()     
 {
         rb.freezeRotation = true; //turn of rigidbody forces for rotation
         //tried this, works if rotate camera x and / or y but not if rotate camera.z
         targetV3 = target.forward; 
         //******** tried this, doesn't work if camera has been rotated, and since object is        
                                      // parented relative position may not be necessary
         //targetV3 = (transform.position - target.position); 
         rotateTo = Quaternion.LookRotation(targetV3); 
         //******** also tried this, same result, doesn't work when camera is rotated
         //rotateTo = Quaternion.identity;
         beamOn = true;  //turns on the Slerp function in Update
 }

}

Thanks for any advice!

By the way, if I pause the game and type 0,0,0 as the eular angle for rotation in the the editor for the object, it faces the camera perfectly, which is why I tried using Quaternion.identity