Error 404

This originally came from Back, Then No Forward, so answer it there.

I found out, that, if I click one of my buttons, this comes up:

TypeError: Error #2007: Parameter child must be non-null.
at flash.display[::]DisplayObjectContainer/removeChild()
at HowToTemplate_fla::MainTimeline/checkForWin()

Then, if you click on it again, another output error comes up:

ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.
at flash.display[::]DisplayObjectContainer/removeChild()
at HowToTemplate_fla::MainTimeline/checkForWin()

Help Thanks! Oh, and, HowToTemplate_fla is the .fla that I’m working on.

Find out how to help at this site. Thanks!

-FlashAj325