error:Object reference not set to an instance of an object

Questions & Answers
1

this is driving me crazy can anyone give me any help please. the error is online 37 in var childcam: Camera

var rocketpref:Transform;
var shoottimer: float = 0;
var shootcooler: float = 0.9;

function OnGUI() {
if(shoottimer> 0){
shoottimer -=0.2* Time.deltaTime * 10;
}

if(shoottimer < 0){
	shoottimer = 0;
}
//Fire button

	if (GUI.Button(Rect(450,280,80,80),"Rockets"))
	{
		if(shoottimer ==0){
					
			var bullit = Instantiate(rocketpref, GameObject.Find("rs").transform.position, Quaternion.identity);
		shoottimer = shootcooler;
		
		}
		
	}
	if (GUI.Button(Rect(350,280,80,80),"cam"))
	{

		var childCam : Camera = bullit.GetComponentInChildren(Camera);
							childCam.enabled =false;
		
	}
}
2

Ok, let me spell it out for you.

// Put this at the top, with the rest of your class variables
private var bullit : GameObject;

// now, in OnGUI, you set 'bullit' to the newly instantiated object
if (GUI.Button(Rect(450,280,80,80),"Rockets"))
{
   if(shoottimer ==0){

       bullit = Instantiate(rocketpref, GameObject.Find("rs").transform.position, Quaternion.identity);
       shoottimer = shootcooler;

   }
}
// Now, you can access 'bullit' because it will exist for more
// than a single GUI cycle, like it would in your original script.
// check for existance of a bullet, first :)
GUI.enabled = (bullit != null);
// Now, the button will only activate if a bullet exists.
if (GUI.Button(Rect(350,280,80,80),"cam"))
{
    var childCam : Camera = bullit.GetComponentInChildren(Camera);
    childCam.enabled = false;
}
GUI.enabled = true;

You need to be aware of variable scope. If a variable is declared inside a set of curly braces, it will exist only inside those braces! If you are modifying a variable inside of an if-statement, you need to make sure that the variable exists outside of that block if you intend to use it elsewhere.

if(condition)
{
    var result = blah;
}
Debug.Log(result); // WILL NOT WORK!

var result = 0;
if(condition)
{
    var result = blah;
}
Debug.Log(result); // Will print 'blah' only on the frame when 'condition' is true

var result = 0;
function Update()
{
    if(condition)
    {
        result = blah;
    }
    Debug.Log(result); // Will print 'blah' on the frame when 'condition' is true,
                       // and then for every frame after that point, because the
                       // scope of 'result' extends *outside* of the function!
}