Hover Script problem

Hello! My name is Unax, and this is my first question, it's this... I have a Hover Script for title screens, but it have an error, how do I fix it? This is the script:

 using System;
 using System.Collections;
 using UnityEngine;
 
 [RequireComponent(typeof (AudioSource))]
 [Serializable]
 public class hoverScript : MonoBehaviour
 {
   public string levelToLoad;
   public AudioClip soundhover;
   public AudioClip beep;
   public bool QuitButton;
 
   public virtual void OnMouseEnter()
   {
     this.audio.PlayOneShot(this.soundhover);
     this.renderer.material.color = Color.red;
   }
 
   public virtual void OnMouseExit()
   {
     this.renderer.material.color = Color.white;
   }
 
   public virtual IEnumerator OnMouseUp()
   {
     return (IEnumerator) new hoverScript.OnMouseUp(this).GetEnumerator();
   }
 
   public virtual void Main()
   {
   }
 }