Script slowing computer message

I had written a script a while ago, that I got to work with no problems, I wanted to make it a bit better/dynamic (boxes can transition left to right or top to bottom), but Im having a problem. I start the script and the tweens start, but I get the error waring me the script wil slow down my computer. I hadn't change the script that drastically so Im not sure why its not working. I tried removing clips, different test but I can't see/trace the problem.

can anybody help?

stop();

import mx.transitions.Tween;

import mx.transitions.easing.*;

Block = new Array();

var Xposition:Number = 0;

var Yposition:Number = 0;

var verticalCount:Number=Math.ceil(Stage.height/30);

var horizontalCount:Number=Math.ceil(Stage.width/30);

var fadeit:Tween;

var scaleitx:Tween;

var scaleity:Tween;

var n:Number = 0;

var valueFromArray:Number

var arrayToRandom:Array = new Array();

var nextSet:Number = 0;

this.createEmptyMovieClip("mcholder", this.getDepth());

//mcholder.swapDepths(1000);

/////places them onto the stage this configuration is sky skyscraper/ reverse for leader

function leftToright ()

{

          for (r=0; r<(verticalCount); r++)

          {

                    for (c=0; c<(horizontalCount); c++)

                    {

                              var particle = mcholder.attachMovie("block","block_"+r+c ,mcholder.getNextHighestDepth());

                              particle._y = Yposition

                              particle._x = Xposition

                              Block = particle;

                              //trace(particle._name)

                              Xposition = Xposition + 30;

                              n++

                    }

                    Xposition = 0;

                    Yposition=Yposition+30;

          }

                    for(var i:Number = 0; i<=horizontalCount-1; i++)

          {

                    arrayToRandom.push(i);

          }

          //RandomArrayToTween ()

}

////////////////////////

function topTobottom ()

{

          for (r=0; r<(horizontalCount); r++)

          {

                    for (c=0; c<(verticalCount); c++)

                    {

                              var particle = mcholder.attachMovie("block","block_"+r+c ,mcholder.getNextHighestDepth());

                              particle._y = Yposition

                              particle._x = Xposition

                              Block = particle;

                              //trace(particle._name)

                              Yposition = Yposition + 30;

                              n++

                    }

                    Yposition = 0;

                    Xposition=Xposition+30;

          }

          ///builds an array with a given number of empty pockets to use as a recrence for random numbers

          //not repeating

          for(var i:Number = 0; i<=verticalCount-1; i++)

          {

                    arrayToRandom.push(i);

          }

          RandomArrayToTween ()

}

//leftToright ()

topTobottom ()

trace(arrayToRandom.length)

trace(arrayToRandom[2])

function randomarray (u)

{

for(var i:Number = 0; i<=numOfChoices-1; i++)

          {

                    arrayToRandom.push( (i+u));

          }

          RandomArrayToTween ()

}

///////////////////////////

function RandomArrayToTween ()

{

          if (arrayToRandom.length > 0)

                    {

                    var randomPos:Number = Math.floor( Math.random() * arrayToRandom.length );

                    var valueFromArray = arrayToRandom.splice(randomPos, 1);

                    var numberRand = parseInt(valueFromArray);

                    tweenblock(numberRand);

                    }

                    else

                    {

                    nextSet=nextSet+arrayToRandom.length

                    stop();

                    randomarray(nextSet);

                    }

}

function tweenblock(n):Void

{

          var fadeit = new Tween(Block, "_alpha", Strong.easeInOut, 100, 0, .5, true);

          var scaleitx = new Tween(Block, "_xscale", Strong.easeInOut, 100, 0, .5, true);

          var scaleity = new Tween(Block, "_yscale", Strong.easeInOut, 100, 0, .5, true);

          fadeit.onMotionChanged = function() {

                    onEnterFrame = function ()

                    {

                              if (n !== Block.length)

                              {

                                        delete onEnterFrame;

  //removeMovieClip.Block;

                                        RandomArrayToTween ()

                              }

                              //else

                              //{

                                        //delete onEnterFrame;

                                        //stop();

                                        //gotoAndPlay(2);

                              //}

                    }

}

}