TypeError: Error #1009, Simple code, SO FRUSTRATING!

programming flash
1

I keep getting this error in my output window.

TypeError: Error #1009: Cannot access a property or method of a null object reference.
	at fractionFishCS4_fla::MainTimeline/frame4()

I started working on this project in cs3 and switched to cs4 if it makes a difference

Heres my code…

var diffArray:Array = new Array();

var dificultyFish:difFish;
diffArray = new Array();

	for(var i:int = 1; i < 4; i++)
	{
		dificultyFish = new difFish();
		addChild(dificultyFish);
		
		dificultyFish.gotoAndPlay(i*10);
		
		with (dificultyFish)
		{
			x = 600;
			y = i * 60 + 40;			
			fishColor = colorChanger(i);
			
			with (difNum)
			{
				difLevel = i;
			}
			fishValue = difLevel;
		}
		
	
	diffArray.push(dificultyFish);	
	}

stop();

somebody please help… i’ve been trying for days and my brain is fried.