demo code

         var vx: int = 0;
         var vy: int = 0;
         var rightInnerBoundary: uint;
         var leftInnerBoundary: uint;
         var topInnerBoundary: uint;
         var bottomInnerBoundary: uint;
         var i;
         var realwallmc: MovieClip;
         var fakewallmc: MovieClip;

          rightInnerBoundary = (stage.stageWidth / 2) + (stage.stageWidth / 4);
          leftInnerBoundary = (stage.stageWidth / 2) - (stage.stageWidth / 4);
          topInnerBoundary = (stage.stageWidth / 2) - (stage.stageWidth / 4);
          bottomInnerBoundary = (stage.stageWidth / 2) + (stage.stageWidth / 4);


        if(!stage){
        this.addEventListener(Event.ADDED_TO_STAGE, stageReady);
    }else{
        stageReady();
    }


    function stageReady(event:Event = null):void {
    stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);
    stage.addEventListener(KeyboardEvent.KEY_UP, keyUpHandler);
    stage.addEventListener(Event.ENTER_FRAME, enterFrameHandler);



             function keyDownHandler(event: KeyboardEvent): void {



                if (event.keyCode == Keyboard.LEFT) {
                    vx = -5;
                    character.gotoAndPlay("WALKL");

                } else if (event.keyCode == Keyboard.RIGHT) {
                    vx = 5;
                    character.gotoAndPlay("WALKR");

                } else if (event.keyCode == Keyboard.UP) {
                    vy = -5;
                    character.gotoAndPlay("WALKR");

                } else if (event.keyCode == Keyboard.DOWN) {
                    vy = 5;
                    character.gotoAndPlay("WALKL");

                }

            }
             function keyUpHandler(event: KeyboardEvent): void {

                if (event.keyCode == Keyboard.LEFT) {
                    vx = 0;
                    character.gotoAndStop("IDLEL");

                }
                if (event.keyCode == Keyboard.RIGHT) {
                    vx = 0;
                    character.gotoAndStop("IDLER");

                }
                if (event.keyCode == Keyboard.UP) {
                    vy = 0;
                    character.gotoAndStop("IDLER");


                }
                if (event.keyCode == Keyboard.DOWN) {
                    vy = 0;
                    character.gotoAndStop("IDLER");
                }
            }

             function enterFrameHandler(event: Event): void

            {

                character.x += vx;
                character.y += vy;
                characterBlock.x = character.x;
                characterBlock.y = character.y;
                Collision.block(characterBlock,fakewallmc);


                for (i = 0; i < 10; i++) {
                realwallmc = background["wall" + (i + 1)];
                fakewallmc = this["wall" + (i+1)];
                fakewallmc.x = realwallmc.x - background.x;
                fakewallmc.y = realwallmc.y - background.y;

                if (character.x < leftInnerBoundary)
                {
                    character.x = leftInnerBoundary;
                    rightInnerBoundary
                    = (stage.stageWidth / 2) + (stage.stageWidth / 4);
                    background.x -= vx;
                }
                else if (character.x + character.width > rightInnerBoundary)
                {
                    character.x = rightInnerBoundary - character.width;
                    leftInnerBoundary
                    = (stage.stageWidth / 2) - (stage.stageWidth / 4);

                    background.x -= vx;
                }
                if (character.y < topInnerBoundary)
                {
                    character.y = topInnerBoundary;
                    bottomInnerBoundary
                    = (stage.stageHeight / 2) + (stage.stageHeight / 4);
                    background.y -= vy;
                }
                else if (character.y + character.height > bottomInnerBoundary)
                {
                    character.y = bottomInnerBoundary - character.height;
                    topInnerBoundary
                    = (stage.stageHeight / 2) - (stage.stageHeight / 4);
                    background.y -= vy;
                }

                //Check the stage boundaries
                if (background.x > 0)
                {
                    background.x = 0;
                    leftInnerBoundary = 0;
                }
                else if (background.y > 0)
                {
                    background.y = 0;
                    topInnerBoundary = 0;
                }
                else if (background.x < stage.stageWidth - background.width)
                {
                    background.x = stage.stageWidth - background.width;
                    rightInnerBoundary = stage.stageWidth;
                }
                else if (background.y < stage.stageHeight - background.height)
                {
                    background.y = stage.stageHeight - background.height;
                    bottomInnerBoundary = stage.stageHeight;
                }


                }

            }
        }