Unity UI text Underlap with gameobject and Nullreference in timer

Question

I am trying to make a 2D brick breaker game in unity .The problems are as follows:

1) The game over text and buttons are getting overlapped by bricks as shown in image:

2) I am getting NullReferencException after I click on Menu button as follows:

NullReferenceException: Object reference not set to an instance of an object
UiManager.Update () (at Assets/UiManager.cs:21)

The UiManager Script is this :

public class UiManager : MonoBehaviour {
    float score=0;
    public Text scoreText;
    public Text endText;
    public Button[] buttons;
    public Text TIMER; 
    float time=30f;

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update () {
        time -=Time.deltaTime;
        TIMER.text = "TIME: " + (int)time;
        if (time < 1) {
            GameOverF ();
            Time.timeScale = 0;
        }
    }

    public void IncrementScore(){

        score++;
        scoreText.text = "SCORE: " + score;
    }

    public void IncrementBadScore(){
        score-=11;
        scoreText.text = "SCORE: " + score;
    }
    public void IncrementGoodScore(){
        score+=11;
        scoreText.text = "SCORE: " + score;
    }


    public void IncrementRedScore(){

            score-=2;
            scoreText.text = "SCORE: " + score;
            }

    public void GameOverF(){
        endText.gameObject.SetActive (true);
        foreach (Button button in buttons) {
            button.gameObject.SetActive (true);

        }


    }

    public void exit(){
        Application.Quit ();
    }

    public void Play(){
        Application.LoadLevel ("level1");
    }
    public void Menu(){

        Application.LoadLevel ("menu");
    }


}

This error is causing my game to hang after I click on Play next time so I have to restart the game only !

line of code is this :

Now how to remove these errors ? I am not able to figure out please help !