Type Coercion failed: cannot convert []#13a355b9 to flash.display.DisplayObject - actionscript-3

Question

I get this error when running, no compile errors.
package {
import flash.display.*;
import flash.events.*;
import flash.utils.*;
public class mainCode extends MovieClip{
//global variables go here
public var circled:Shape = new Shape();
public var circled2:Shape = new Shape();
public var circled3:Shape = new Shape();
public var angled:int = new int();
public var circlearray1:Array = new Array(4);
public var circlearray2:Array = new Array(4);
public function mainCode(){
makeCircle(circled, 100);
makeCircle(circled2, 50);
makeCircle(circled3, 50);
for(var i:int=0; i<4; i++){circlearray1[i] = new Array(20);}
for(var n:int=0; n<4; n++){circlearray2[n] = new Array(20);}
stage.addEventListener(Event.ENTER_FRAME, mainLoop);
}
//functions go here
private function mainLoop(e:Event){
trace(1);
angled+=1;
angled%=360;
circled.x = stage.stageWidth / 2;
circled.y = stage.stageHeight/ 2;
circled2.x = circled.x + 100*Math.cos(radians(angled));
circled2.y = circled.y + 100*Math.sin(radians(angled));
circled3.x = circled.x + 100*Math.cos(radians((angled + 180) % 360));
circled3.y = circled.y + 100*Math.sin(radians((angled + 180) % 360));
trace(2);
for (var i:int = 0; i < 4; i++)
{
trace(3);
if (circlearray1[i][0] != undefined)
{removeChild(circlearray1[i][0]);}
if (circlearray2[i][0] != undefined)
{removeChild(circlearray2[i][0]);}
trace(4);
for (var m:int = 0; m < 19; m++)
{
circlearray1[i][m] = circlearray1[m+1];
circlearray2[i][m] = circlearray2[m+1];
}
circlearray1[i][19] = new Shape();
circlearray2[i][19] = new Shape();
makeCircle(circlearray1[i][19], 25);
makeCircle(circlearray2[i][19], 25);
circlearray1[i][19].x = circled2.x + 50*Math.cos(radians(((-angled + (i*90)) * 2) % 360));
circlearray1[i][19].y = circled2.y + 50*Math.sin(radians(((-angled + (i*90)) * 2) % 360));
circlearray2[i][19].x = circled3.x + 50*Math.cos(radians(((-angled + (i*90)) * 2) % 360));
circlearray2[i][19].y = circled3.y + 50*Math.sin(radians(((-angled + (i*90)) * 2) % 360));
trace(8);
}
}
private function makeCircle(circles:Shape, radius:int)
{
circles.graphics.clear();
circles.graphics.lineStyle(2,0x000000);
circles.graphics.beginFill(0x990000);
circles.graphics.drawCircle(0,0,radius);
circles.graphics.endFill();
addChild(circles);
}
private function degrees(radians:Number):Number
{
return radians * 180/Math.PI;
}
private function radians(degrees:Number):Number
{
return degrees * Math.PI / 180;
}
private function killCircle(circlei:Shape):void {
removeChild(circlei);
}
}
}
I've traced it down to {removeChild(circlearray1[i][0]);}, which seems to be returning the error. I have no idea why it's doing this, I've tried alternatives such as circlearray1[i][0].parent.removeChild(circlearray1[i][0]); and if (circlearray1[i][0] is Shape) ... , but no dice.
For reference, I'm trying to make some circles circle around other circles, but have the outermost circles leave an "image lag" (or afterimage) while moving. I do this by creating objects and deleting them using for loops and multidimensional arrays, as I dont feel like typing out 50 create object calls manually and edit each one manually.

Answer 1

Probably, this part:
for (var m:int = 0; m < 19; m++)
{
circlearray1[i][m] = circlearray1[m+1];
circlearray2[i][m] = circlearray2[m+1];
}
You assign to endpoint elements, which you initially assume to be Shapes the elements which are Arrays. Then later you go at circlearray1[i][0] assuming it is Shape if it is not empty, but it is already an Array due to the assignment above. It's probably a typo and you meant this:
for (var m:int = 0; m < 19; m++)
{
circlearray1[i][m] = circlearray1[i][m+1];
circlearray2[i][m] = circlearray2[i][m+1];
}
There's actually a more clean way to do that. Array in AS3 is a lot like C# ArrayList, you can insert elements to either end and extract elements from either end without re-indexing elements manually:
trace(3);
// If you are sure the first element is not empty
// you can get its reference removing them from
// the Array at the same time.
removeChild(circlearray1[i].shift());
removeChild(circlearray2[i].shift());
trace(4);
// All Array elements are automatically shifted
// by -1 so you don't need to move each of them manually.
circlearray1[i][19] = new Shape();
circlearray2[i][19] = new Shape();