Null Object Reference Error Problem

Here's the game loop function where I am having the problem and below that is the function where added the _pauseSound to the _gameModel.screen Sprite. I first tried to remove _pauseSound with this:

_gameModel.screen.removeChild(_pauseSound); but I get a #2025 Error: supplied DisplayObject must be a child of the caller, so I changed it to _pauseSound.parent.removeChild(_pauseSound); and I get the null object error. I have _pauseSound instantiated at the top of the page so I don't know what the problem is.

public function runGameEnterFrame(e:Event):void {

                              trace("_pauseSound = "+_pauseSound);

                                        screenText.update();

                                        timeDifference = getTimer() - lastTime;

                                        lastTime = getTimer();

                                        checkSystemState();

                                        systemFunction();

                                        frameCounter.countFrames();

                                        if(_gameModel.updateMusVol){

                                                  soundController.updateSoundVolume(true);

                                        }

                                        if(_gameModel.updateSoundVol){

                                                  soundController.updateSoundVolume(false);

                                        }

                                        if(_gameModel.gotoIntro){

                                                  _docClass.gotoAndStop(1);

                                                  trace("_pauseSound2 = "+_pauseSound);

                                                  trace("_pauseSound.parent = "+_pauseSound.parent);-------This is 'null'

                                                  trace("_gameModel.screen = "+_gameModel.screen );

                                                  _pauseSound.parent.removeChild(_pauseSound);-----error

                                                  _gameModel.pauseAndMuteAdded = false;

                                                  _levelTwo.dispose();

                                                  _gameModel.gotoIntro = false;

                                                  }

                    }

public function addPauseEtc():void{

                              if(_gameModel.pauseAndMuteAdded == false){

                                                  _pauseSound.addPauseSoundButtons(470,20,500,20,540,20,580,20);

                                                            _gameModel.screen.addChild(_pauseSound);

                                                            _gameModel.pauseAndMuteAdded = true;

                                                  }

                    }