Null reference exception error in Unity, Please Help!

I have created a script earlier today and in mono develop it showed no errors but when I tested it it gave me the error: NullReferenceException: Object reference not set to an instance of an object CharacterGenerator.DisplayVitals() CharacterGenerator.OnGUI()
Here is my script which is producing the error:

using UnityEngine;
using System.Collections;
using System;

public class CharacterGenerator : MonoBehaviour {
private PlayerCharacter _toon;

// Use this for initialization
void Start () {
    _toon = new PlayerCharacter();
	_toon.Awake();
}

// Update is called once per frame
void Update () {

}

void OnGUI() {
	DisplayName ();
	DisplayAttributes();		
	DisplayVitals();
	DisplaySkills();
}

private void DisplayName() {
	GUI.Label (new Rect(10, 10, 50, 25), "Name:");
	_toon.Name = GUI.TextArea(new Rect(65, 10, 100,25), _toon.Name);
}

private void DisplayAttributes() {
	for(int cnt = 0; cnt < Enum.GetValues(typeof(AttributeName)).Length; cnt++) {
		GUI.Label(new Rect(10, 40 + (cnt * 25), 100, 25), ((AttributeName)cnt).ToString());
	    GUI.Label(new Rect(115, 40 + (cnt * 25), 30, 25), _toon.GetPrimaryAttribute(cnt).AdjustedBaseValue.ToString());
	}
}

private void DisplayVitals() {
	for(int cnt = 0; cnt < Enum.GetValues(typeof(VitalName)).Length; cnt++) {
		GUI.Label(new Rect(10, 40 + ((cnt + 7) * 25), 100, 25), ((VitalName)cnt).ToString());
	    GUI.Label(new Rect(115, 40 + ((cnt + 7) * 25), 30, 25), _toon.GetVital(cnt).AdjustedBaseValue.ToString());
	}
}

private void DisplaySkills() {
	for(int cnt = 0; cnt < Enum.GetValues(typeof(SkillName)).Length; cnt++) {
		GUI.Label(new Rect(250, 40 + (cnt * 25), 100, 25), ((SkillName)cnt).ToString());
	    GUI.Label(new Rect(355, 40 + (cnt * 25), 30, 25), _toon.GetSkill(cnt).AdjustedBaseValue.ToString());
	}
}

}

Have you Got VitalName on another script??? If so it looks as though GUI is trying to access an Enum, without any luck.I dont know how long it is, but you may need to rewrite the Vital Name section. BTW is this a burgzerg/ petey script, i ask because of the _toon. If it is check out youtube comments for the tutorial, might help.