as3 matching game helppppppppppppppp

1

this my could for matching game but i dont know why i get this error in my out put chanel :

TypeError: Error #1006: startFlip is not a function.
at MatchingGameObject11/returnCards()
at MatchingGameObject11/clickCard()

please help me :hangover:

package {
import flash.display.;
import flash.events.;
import flash.text.*;
import flash.utils.getTimer;
import flash.utils.Timer;
import flash.media.Sound;
import flash.media.SoundChannel;

public class MatchingGameObject11 extends MovieClip {
	// game constants
	private static const boardWidth:uint = 6;
	private static const boardHeight:uint = 6;
	private static const cardHorizontalSpacing:Number = 52;
	private static const cardVerticalSpacing:Number = 52;
	private static const boardOffsetX:Number = 145;
	private static const boardOffsetY:Number = 70;
	private static const pointsForMatch:int = 100;
	private static const pointsForMiss:int = -5;
	
	// variables
	private var firstCard:Card10;
	private var secondCard:Card10;
	private var cardsLeft:uint;
	private var gameScore:int;
	private var gameStartTime:uint;
	private var gameTime:uint;
	
	// text fields
	private var gameScoreField:TextField;
	private var gameTimeField:TextField;
	
	// timer to return cards to face-down
	private var flipBackTimer:Timer;
	
	// set up sounds
	var theFirstCardSound:FirstCardSound = new FirstCardSound();
	var theMissSound:MissSound = new MissSound();
	var theMatchSound:MatchSound = new MatchSound();


	// initialization function
	public function MatchingGameObject11():void {
		// make a list of card numbers
		var cardlist:Array = new Array();
		for(var i:uint=0;i<boardWidth*boardHeight;i++) {
			cardlist.push(i);
		}
		
		// create all the cards, position them, and assign a randomcard face to each
		cardsLeft = 0;
		for(var x:uint=0;x<boardWidth;x++) { // horizontal
			for(var y:uint=0;y<boardHeight;y++) { // vertical
				var c:Card10 = new Card10(); // copy the movie clip
				c.stop(); // stop on first frame
				c.x = x*cardHorizontalSpacing+boardOffsetX; // set position
				c.y = y*cardVerticalSpacing+boardOffsetY;
				var r:uint = Math.floor(Math.random()*cardlist.length); // get a random face
				c.cardface = cardlist[r]; // assign face to card
				cardlist.splice(r,1); // remove face from list
				c.addEventListener(MouseEvent.CLICK,clickCard); // have it listen for clicks
				c.buttonMode = true;
				addChild(c); // show the card
				cardsLeft++;
			}
		}
		
		// set up the score
		gameScoreField = new TextField();
		addChild(gameScoreField);
		gameScore = 0;
		showGameScore();
		
		// set up the clock
		gameTimeField = new TextField();
		gameTimeField.x = 450;
		addChild(gameTimeField);
		gameStartTime = getTimer();
		gameTime = 0;
		addEventListener(Event.ENTER_FRAME,showTime);
	}
	
	// player clicked on a card
	public function clickCard(event:MouseEvent) {
		var thisCard:Card10 = (event.target as Card10); // what card?
		
		if (firstCard == null) { // first card in a pair
			firstCard = thisCard; // note it
			thisCard.startFlip(thisCard.cardface+2);
			playSound(theFirstCardSound);
			
		} else if (firstCard == thisCard) { // clicked first card again
			firstCard.startFlip(1);
			firstCard = null;
			playSound(theMissSound);
			
		} else if (secondCard == null) { // second card in a pair
			secondCard = thisCard; // note it
			thisCard.startFlip(thisCard.cardface+2);
				
			// compare two cards
			if (Math.floor(firstCard.cardface/2) == Math.floor(secondCard.cardface/2)) {
				// remove a match
				removeChild(firstCard);
				removeChild(secondCard);
				// reset selection
				firstCard = null;
				secondCard = null;
				// add points
				gameScore += pointsForMatch;
				showGameScore();
				playSound(theMatchSound);
				// check for game over
				cardsLeft -= 2; // 2 less cards
				if (cardsLeft == 0) {
					MovieClip(root).gameScore = gameScore;
					MovieClip(root).gameTime = clockTime(gameTime);
					MovieClip(root).gotoAndStop("gameover");
				}
			} else {
				gameScore += pointsForMiss;
				showGameScore();
				playSound(theMissSound);
				flipBackTimer = new Timer(2000,1);
				flipBackTimer.addEventListener(TimerEvent.TIMER_COMPLETE,returnCards);
				flipBackTimer.start();
			}
			
		} else { // starting to pick another pair
			returnCards(null);
			playSound(theFirstCardSound);
			// select first card in next pair
			firstCard = thisCard;
			firstCard.startFlip(thisCard.cardface+2);
		}
	}
	
	// return cards to face-down
	public function returnCards(event:TimerEvent) {
		firstCard.startFlip(1);
		secondCard.startFlip(1);
		firstCard = null;
		secondCard = null;
		flipBackTimer.removeEventListener(TimerEvent.TIMER_COMPLETE,returnCards);
	}
	
	public function showGameScore() {
		gameScoreField.text = "Score: "+String(gameScore);
	}
	
	public function showTime(event:Event) {
		gameTime = getTimer()-gameStartTime;
		gameTimeField.text = "Time: "+clockTime(gameTime);
	}
	
	public function clockTime(ms:int) {
		var seconds:int = Math.floor(ms/1000);
		var minutes:int = Math.floor(seconds/60);
		seconds -= minutes*60;
		var timeString:String = minutes+":"+String(seconds+100).substr(1,2);
		return timeString;
	}
	
	public function playSound(soundObject:Object) {
		var channel:SoundChannel = soundObject.play();
	}
}

}