Why is my game crashing when I create a new Stack?

My game crashes when I press play in the editor after switching from scenes. I narrowed down the problem and it originates in the awake() method of my ScoreManager class when a new stack is created. How can I fix this? Here is the class:

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.Threading;

public class ScoreManager : MonoBehaviour 
{
	public GUIText score;

	public GUIText scoreShadow;
	
	private int currentScore = 0;
	public int scoreToUpdate = 0;
	
	private Stack<int> stack;

	private Thread t1;
	private bool isDone = false;

	void Awake() 
	{
		stack = new Stack<int>();
		t1 = new Thread(updateScore);
		t1.Start();
	}

	private void updateScore()
	{
		while(true)
		{
			if(stack.Count > 0)
			{
				int newScore = stack.Pop();



				for(int i = currentScore; i < newScore; i++){
					Thread.Sleep(1); //ms
					scoreToUpdate = i;
				}
				currentScore = scoreToUpdate;
			}
			
			if(isDone)
				return;
		}
	}

	void Update() 
	{
		score.text = scoreToUpdate + "";
		scoreShadow.text = scoreToUpdate + "";
	}

	public void addScore(int point)
	{
		stack.Push(point);
	}
	
	public void OnApplicationQuit()
	{
		isDone = true;
		t1.Abort();
	}

}

Try maybe:

t1 = new Thread(new ThreadStart(updateScore));

Also it is always a good idea to use try…catch.