Centerd PopUp-Help-Minor Change AS2

Hi folks
This tutorial http://www.kirupa.com/developer/mx/centered_popup.htm works just fine. But, I am using this on a button inside of moiveclip1, which lives in movieclip2, which lives in movieclip3, which is on the main timeline. So when I launch my main movie, the button does not launch the pop up. I am assuming it has something to do with the reference to “_root” in this code:

_root.openWinCentre = function (url, winName, w, h, toolbar, location, directories, status, menubar, scrollbars, resizable) {
getURL ("javascript:var myWin; if(!myWin || myWin.closed){myWin = window.open('" + url + "','" + winName + "','" + "width=" + w + ",height=" + h + ",toolbar=" + toolbar + ",location=" + location + ",directories=" + directories + ",status=" + status + ",menubar=" + menubar + ",scrollbars=" + scrollbars + ",resizable=" + resizable + ",top='+((screen.height/2)-(" + h/2 + "))+',left='+((screen.width/2)-(" + w/2 + "))+'" + "')}else{myWin.focus();};void(0);");
}

When this button is placed in the root timeline is functions fine, but not at all when used inside my movieclip1, which lives in movieclip2 which lives in movieclip3 on the main timeline. Any Ideas ?

Thank you in advance !!