Virtical rotation script errors.

Hi trying to create a simple rotation script to rotate my object up and down.though when i remove the "Horizontal" movment of this script it gets errors when i only want the vertical rotation.

 using UnityEngine;
 using System.Collections;
 
 public class climbDive : MonoBehaviour {
 
         
     void Update () {
         
         transform.Rotate (  Input.GetAxis ("Vertical"), 0.0f);
         
         
     }
     
 }