Unity C#对象引用未设置为对象的实例

我一直在第64行得到错误Object引用没有设置为对象的实例，我不知道我需要做什么

一切都在运转，就像生命出现了，计时器和分数都在，但分数没有增加，如果你能告诉我出了什么问题，我会非常感谢

这是我的代码：

using UnityEngine;
using System.Collections;
public class Player : MonoBehaviour {
private CountdownTimer myTimer;
private int score = 0;
private int lives = 3;
private int DEATH_Y = -10;
public Texture2D LivesLeft1;
public Texture2D LivesLeft2;
public Texture2D LivesLeft3;
public int GetScore(){
    return score;
}
public int GetLives()
{
    return lives;
}
private void Start()
{
    myTimer = GetComponent<CountdownTimer>();
}
private void Update()
{
    float y = transform.position.y;
    if (y < DEATH_Y) {
        MoveToStartPosition();
        lives--;
    }
    if (score == 10)
    {
        Application.LoadLevel("Level2");
    }
    if (lives == 0)
    {
        Application.LoadLevel("GameOver");
    }
}
private void OnGUI()
{
    GUILayout.BeginHorizontal ();
    DisplayLives();
    int secondsLeft = myTimer.GetSecondsRemaining();//this is line 64
    string timeMessage = "Seconds left = " + secondsLeft;
    GUILayout.Label(timeMessage);
    string scoreMessage = "Score = " + score;
    GUILayout.Label (scoreMessage);
}
private void DisplayLives()
{
    int playerLives = GetLives();
    if (1 == playerLives) {
        GUILayout.Label(LivesLeft1);
    }
    if (2 == playerLives) 
    {
        GUILayout.Label(LivesLeft2);
    }
    if(3 == playerLives){
        GUILayout.Label(LivesLeft3);
    }
}
private void MoveToStartPosition()
{
    Vector3 startPosition = new Vector3(0,5,0);
    transform.position = startPosition;
}
/**
 * what increases the score
 * anything with the tag Hidden
*/
private void OnTriggerEnter(Collider c)
{
    string tag = c.tag;
    if("Hidden" == tag)
    {
        score++;
    }
}
}