I need help, Everytime i put my scense in play it says, "Object reference not set to an instance of an object". Advice would be great:)

Questions & Answers
1

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class MainMenu : MonoBehaviour
{
public Canvas quitmenu;
public Button exitbutton;

void Start()
{
	quitmenu = quitmenu.GetComponent<Canvas>();
	exitbutton = quitmenu.GetComponent<Button>();
}

public void exitpress()
{
	quitmenu.enabled = true;
	exitbutton.enabled = false;
}

public void nopress()
{
	quitmenu.enabled = false;
	exitbutton.enabled = true;
}

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

}

I found everytime i played the exit button would remove its self from the script component’s. I put it back will in play still nothing. Checked the function in the button component it was good, also the script component is on the canvas.

2

This means that either the canvas component or the button is non existent in your quitmenu GameObject, or the quitmenu Gameobject itself is not referenced.
In fact, because you are making the canvas public and most likely setting it in the inspector, you can remove the first line of the start function.
In addition, I am assuming that your button is a child of your canvas, in which case you should use GetComponentInChildren for the button.