Using navigateUrl in flex values are not posting to sercerside

Question

Hi when i try with navigate url it is working but one problem I am facing .it is very critical for me. When I am posting one value to jsp.with urlVariables through method=POST values are not getting in jsp, null values getting and window is opening, why i used this navigate only if i open using externainterface new window is creating and session is not maintaining,please help in this. my code is,

private function openNewWindow(event:MouseEvent, url:String, winName:String, w:int, h:int, toolbar:int, location:int, directories:int, status:int, menubar:int, scrollbars:int, resizable:int):void {

              var fullURL:String = "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);"; var u:URLRequest = new URLRequest(fullURL); var variables:URLVariables = new URLVariables(); variables.cntrl_flag = "Admin"; u.method = URLRequestMethod.POST; u.data = variables;
navigateToURL(u,"_self");

           }

Thanks in Advance