Using MovieClip(root) Problem

im at frame 3.. i have text field on the stage name scoreTxt.. at frame 3 i added TryClass..

TryClass has function of updateScore..  so my code is

public function updateScore(amount:int):void

                    {

                              score += amount;

                              if(score < 0) score = 0;

                              realNumber = score;

                              setInterval(updateDisplayedScore, 10);

                              var displayedNumber:Number = 0;

                              function updateDisplayedScore():void

                              {

                              displayedNumber += Math.round((realNumber-displayedNumber)/5);

                              if (realNumber - displayedNumber < 5 && realNumber - displayedNumber > -5)

                              {

                              displayedNumber = realNumber;

                              }

                              addZeros();

                              }

                              function addZeros():void

                              {

                              var str:String = displayedNumber.toString();

                              MovieClip(root).scoreTxt.text = str; <------ i use MovieClip(root) as i saw from internet..its working fine.. but

                              }

                    }

but then if for example .. the user died or he reaches the required score.. im suppose to go a certain frame using this code..

MovieClip(this.root).gotoAndStop("Main");

its reaching the frame "Main" but its pointing errors to this --> MovieClip(root).scoreTxt.text

that "Main" frame is on frame 4.. which i did not yet added the TryClass.. should i add to all my frames the TryClass? and how is that?

Sorry for the question.. i dont know yet how to perfectly code in the class.. and accessing the timelines and other external class.. Please dont use deeper language of actionscript.. on a beginner way only..