"Error#2025 The supplied DisplayObject must be a child of the caller." upon trying to removeChild(); - actionscript-3

Question

I'm creating a simple iPhone game (but the class I'm in is requiring me to use Flash...), and I'm having a major issue as I'm trying to remove objects from the game.
The game is somewhat of a dynamic time-wasting bubblewrap game where there are infinite "refreshes" of the stage. Once the user pops all the bubbles, more randomly generate. (When the array is empty, call the setup() again.)
For now, I have one of each five different colored bubble graphics pulled from the library by code and placed on the stage randomly. However, I don't like the overlap, so I've given each bubble a small square hitspace so when they're placed randomly and overlap significantly they pop themselves. For some reason when I'm trying to remove the bubbles it gives me
Error#2025 The supplied DisplayObject must be a child of the caller.
I've tried adding stage to addChild and removeChild, but I get the same error.
import flash.events.*;
import flash.display.*;
var bubbles:Array = new Array();
var b:BlueBubble = new BlueBubble();
var b2:GreenBubble = new GreenBubble();
var b3:PinkBubble = new PinkBubble();
var b4:PurpleBubble = new PurpleBubble();
var b5:YellowBubble = new YellowBubble();
// values to be tweaked later
var bNum:uint = 1;
var maxSize:uint = 100;
var minSize:uint = 1;
var range:uint = maxSize - minSize;
var tooBig:uint = 100;
function init():void {
setup();
stage.addEventListener(Event.ENTER_FRAME, onEveryFrame);
}
function setup():void {
for (var i:uint=0; i<bNum; i++) {
// blue
b.width = Math.ceil(Math.random() * range) + minSize;
b.height = b.width;
b.x = Math.random()*(stage.stageWidth - b.width);
b.y = Math.random()*(stage.stageHeight - b.height);
bubbles.push(b);
stage.addChild(b);
// green
b2.width = Math.ceil(Math.random() * range) + minSize;
b2.height = b2.width;
b2.x = Math.random()*(stage.stageWidth - b2.width);
b2.y = Math.random()*(stage.stageHeight - b2.height);
bubbles.push(b2);
stage.addChild(b2);
// pink
b3.width = Math.ceil(Math.random() * range) + minSize;
b3.height = b3.width;
b3.x = Math.random()*(stage.stageWidth - b3.width);
b3.y = Math.random()*(stage.stageHeight - b3.height);
bubbles.push(b3);
stage.addChild(b3);
// purple
b4.width = Math.ceil(Math.random() * range) + minSize;
b4.height = b4.width;
b4.x = Math.random()*(stage.stageWidth - b4.width);
b4.y = Math.random()*(stage.stageHeight - b4.height);
bubbles.push(b4);
stage.addChild(b4);
// yellow
b5.width = Math.ceil(Math.random() * range) + minSize;
b5.height = b5.width;
b5.x = Math.random()*(stage.stageWidth - b5.width);
b5.y = Math.random()*(stage.stageHeight - b5.height);
bubbles.push(b5);
stage.addChild(b5);
//add event listeners for bubbles later
}
}
function onEveryFrame(e:Event) {
for (var i:uint=0; i<bubbles.length; i++) {
bubbles[i].width++;
bubbles[i].height++;
if (bubbles[i].height >= tooBig && bubbles[i].width >= tooBig) {
bubbles[i].height = tooBig;
bubbles[i].width = tooBig;
}
// Blue hit testing
if (b2.hitGreen.hitTestObject(b.hitBlue)) {
removeChild(b);
}
if (b3.hitPink.hitTestObject(b.hitBlue)) {
removeChild(b);
}
if (b4.hitPurple.hitTestObject(b.hitBlue)) {
removeChild(b);
}
if (b5.hitYellow.hitTestObject(b.hitBlue)) {
removeChild(b);
}
// Other hit testing...
}
}
init();

Answer 1

You are adding b, b2, b3, etc to the stage, but removing them from whatever object is executing this code. Try changing
stage.addChild(b);
to
addChild(b);
Additionally, it is a good idea to check that an object is a child before removing it. Try changing
if (...)
removeChild(b);
to
if (contains(b) && ...)
removeChild(b);

Answer 2

The best way to solve this is:
mc.parent.removeChild(mc);
Basically, the removeChild function needs to be called from whatever display object that your soon to be removed object is in.