OnMouseUp error

Ok so im getting an error with a script that i have used before and i cant figure out what too do to fix the issue. The script im using (ill post it below) highlights text options (3d text) when i scroll over them (which works). But The ability to click on the text and for it to do something wont work. I tried using Input.Getbutton, and OnMouseUp() but neither seemed to work.

I keep getting this error

NullReferenceException: Object reference not set to an instance of an object hover Script.OnMouseExit () (at Assets/Resources/NewScripts/hover Script.js:10) UnityEngine.SendMouseEvents:DoSendMouseEvents()

This is the script

[CODE]ar levelToLoad : String; var soundhover : AudioClip; var beep : AudioClip; var QuitButton : boolean = false;

function OnMouseEnter() { audio.PlayOneShot(soundhover); renderer.material.color = Color.green; }

function OnMouseExit() { renderer.material.color = Color.white; }

function OnMouseUp() { audio.PlayOneShot(beep); yield new WaitForSeconds(0.35); if(QuitButton) { Application.Quit(); } else { Application.LoadLevel(levelToLoad); } } @script RequireComponent(AudioSource)[/CODE]