MovieClip not responding to a function

Question

I have a complicated problem that I don't know where it comes from. I have three movie clip in my first frame that each one call "homework" function.

Problem:
There is something wrong with the third one that if you click on it first it works correctly, but if you click on the other objects and then come back and try third one it doesn't work anymore.

I don't have this problem with the others MovieClip objects so how is this problem possible for third MC using the exact same function?

Here is the homeWork function:

function homeWork(a :int) :void
{
    gotoAndStop(2);
    cubeContainer.addChild(movieClip);
    movieClip.x= 20;
    movieClip.y= 20;
    var j:int =0;

    for( var i = a; i < (a+10); i++)
    {
        cubeContainer.addChild(photos[i]);
        photos[i].width = 130;
        photos[i].height = 130;
        photos[i].x = j-80;
        photos[i].y = stage.height-photos[i].height;
        j += 90;
        photos[i].doubleClickEnabled=true;
        photos[i].addEventListener(MouseEvent.DOUBLE_CLICK ,covering);
        dragAndDrop(photos[i]);
    }
}