Unknown Identifier Problem UnityScript

Here is my script the error I am getting is: Assets/Scripts/Menu2.js(11,20): BCE0005: Unknown identifier: ‘menuSkin’.

var beep : AudioClip;
var GUISkin : GUISkin;
var menuArea : Rect;
var playButton : Rect;
var instructionsButton : Rect;
var quitButton : Rect;

function OnGUI(){
	GUI.skin = menuSkin;
	GUI.BeginGroup (menuArea);
	
	if(GUI.Button(Rect(playButton), "Play"))
	{
	  audio.PlayOneShot(beep);
	}
	if(GUI.Button(Rect(instructionsButton), "Instructions")) 
	{
	audio.PlayOneShot(beep);
	}
	if(GUI.Button(Rect(quitButton), "Quit"))
	{
	audio.PlayOneShot(beep);
	}
	
}

@script RequireComponent(AudioSource)

you haven’t declared the variable menuSkin. change the variable up the top from

var GUISkin : GUISkin;

to

var menuSkin : GUISkin;

You have no variable called “menuSkin”. You have one called “GUISkin”, but it’s probably not a good idea to name a variable the same thing as a type.