Cannot Display Source Code At This Location

programming flash
1

Here’s a sample code I tried to create an instance via AS:

var a:MovieClip = new ball();
a.name = "test";
addChild(a);
a.x = 200;
a.y = 200;
trace(a);
trace(a.name);

It works fine, the ball shows up on the stage. Nothing’s wrong with it until I try to debug (Ctrl + Shift+ Enter) to understand it clearer and here’s what I got"

Cannot display source code at this location

after the line

var a:MovieClip = new ball();

.

I dont know if it influents anything if I keep coding on big project. I hope any of you who has deep knowledge can clear me up. That’d be really appreciated.