1009 null object reference

Hi, I'm creating an android game and everything goes wrong when you lose and the "lose screen" is displayed...

TypeError: Error #1009: Cannot access a property or method of a null object reference.

          at rock/destroyEnemy()

          at Function/main/$construct/endGame()

          at Function/main/$construct/Loop()

(this is in the main class file)

for each (var enemy:rock in aEnemyArray)

                                        {

                                                  //destroy enemy in loop

                                                  enemy.destroyEnemyAgain();

                                                  //remove enemy from array

                                                  aEnemyArray.splice(0, 1);

                                        }

(this is in the enemy class file)

public function destroyEnemy():void

                    {

   parent.removeChild(this)

   removeEventListener(Event.ENTER_FRAME, enemyLoop);

                    }

The thing is that if you don't shot at he rocks there´s no problem, but when you hit one, at the time you lose, the error comes.

Thanks.