hitTestObject issue // remove stage Error #2025 - actionscript-3

Question

hey :S I`m trying to make 2 things so far but neither work :(
The 1st is to make an Row of 5 Ships that position them selves from the top to left.Then add an Event to make them move down.
But every time i try to make a new Row of 5 new ships ... they position themselves after the last ship from the previous Row.I did think of a way to fix that by waiting the 1st Row of ships to go beyond the stage and then remove them from the stage and splice from the Array but ... when I increase the speed of spawning (when i have 2 rows with 5 ships on the stage or more)that does't work.
And the second error I think is from that fact .... that I have 2 rows at the same time on the stage.
ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.
at flash.display::DisplayObjectContainer/removeChild()
at MainClass/doShips()
at MainClass/everyFrame()
I dont know what exactly to paste from the code so i had to push everything in the MainClass of the FLA.fail :D but i did it neatly! so if anyone helped me he would track the code easily
so its a simple FLA.fail with 4 MC and in those 4 MC there is no code
a Bullet
a Ship with colour Yellow
a Ship2 with colour Green so i can see the randomising
and a Player with the class Turret
so the MainClass of the FLA is :
package {
import flash.display.MovieClip;
import flash.events.Event;
import flash.events.MouseEvent;
public class MainClass extends MovieClip {
protected var mouseSpeed:Number = 20;
protected var _thePlayer:Turret = new Turret();
protected var shipCount:Number;
protected var shipCount2:Number;
protected var shipArray:Array = new Array();
protected var counter:int = 0;
//variables for bullets
private var shootCooldown:Number = 0; //speed of the fire
private var firing:Boolean = false;//bullets triger
private var numToShoot:int = 1; //bullets
const MAX_COOLDOWN = 10; //bullets timer
protected var _bulletsArray:Array = new Array();
public function MainClass() {
_thePlayer.x = stage.stageWidth/2
_thePlayer.y = stage.stageHeight - _thePlayer.height/2
addChild(_thePlayer)
addEventListener(Event.ENTER_FRAME, everyFrame)
stage.addEventListener(MouseEvent.MOUSE_DOWN, startFire);
stage.addEventListener(MouseEvent.MOUSE_UP, stopFire);
}
private function startFire(ev:MouseEvent) {
firing = true;
}
private function stopFire(ev:MouseEvent) {
firing = false;
}
//every frame do this
protected function everyFrame(ev:Event):void{
//Moving The Turret
moveTheTurret();
//increase the counter every frame
counter++;
if(counter % 70 == 0){
//position the ships on the stage
positionShips();
}
//handle the ships when they are added on the stage
doShips();
//when to fire
updateFire();
//handle the bullets
doBullets();
}
//Moving The Turret
protected function moveTheTurret() {
if (mouseX > _thePlayer.x +15) {
_thePlayer.x += mouseSpeed;
} else if (mouseX < _thePlayer.x - 15) {
_thePlayer.x -= mouseSpeed;
} else {
_thePlayer.x = mouseX;
}
}
//createShips and position them
protected function positionShips() {
shipCount = 3;
shipCount2 = 2;
var gap = 10;
for (var i:int = 0; i < shipCount; i++) {
var s = new Ship();
shipArray.push(s);
}
for (var j:int = 0; j < shipCount2; j++) {
s = new Ship2();
shipArray.push(s);
}
var array:Array=new Array();
while (shipArray.length>0) {
var index:uint = Math.floor(Math.random() * shipArray.length);
array.push(shipArray[index]);
shipArray.splice(index,1);
}
shipArray = array;
//shipsArray has been randomized
for (var k:int = shipArray.length - 1; k >= 0; k--) {
addChild(shipArray[k]);
shipArray[k].x = shipArray[k].width/2 + (shipArray[k].width * k) + (gap*k);
}
}
//move the ships
protected function doShips() {
for (var i:int = shipArray.length - 1; i >= 0; i--) {
shipArray[i].y +=3 //make the Ships fall down
for (var bcount= _bulletsArray.length-1; bcount >= 0; bcount--) {
//if the bullet is touching the ship
if (shipArray[i].hitTestObject(_bulletsArray[bcount])) {
//if we get here it means there`s is a collision
removeChild(_bulletsArray[bcount]);
_bulletsArray.splice(bcount,1);
removeChild(shipArray[i]);
_bulletsArray.splice(i,1);
}
}
//if it gets over 380 remove from stage and splice from the array
if(shipArray[i].y > 380){ // stage.stageHeight)
removeChild(shipArray[i]);
shipArray.splice(i,1);
}
}
}
//when to fire
public function updateFire() {
//if we are currently holding the mouse down
if(firing == true){
fire();
}
//reduce the cooldown by 1 every frame
shootCooldown--;
}
//Shoot bullets
private function fire() {
if (shootCooldown <= 0) {
//reset the cooldown
shootCooldown = MAX_COOLDOWN
for (var i=0; i<numToShoot; i++){
//spown a bullet
var b = new Bullet();
//set the rotation of the bullet
b.rotation = -90
b.x = _thePlayer.x;
b.y = _thePlayer.y;
//add the bullet to the list/Array of _bulletsArray
_bulletsArray.push(b);
//add the bullet to the perent object;
addChild(b);
}
}
}
//handling the bullets
protected function doBullets(){
//make a for loop to iterate all the _bulletsArray on the screen
for (var bcount:int = _bulletsArray.length-1; bcount>=0; bcount--) {
//make the bullets move Up
_bulletsArray[bcount].y -=20;
//if the bullet is beyond the screen remove from the stage and the Array
if(_bulletsArray[bcount].y < 0){
removeChild(_bulletsArray[bcount])
_bulletsArray.splice(bcount,1);
}
}
}
}
}
I dont know how to fix neither of the 2 problems.Would be very thankful for any help!!!
Thanks in advance.