ReferenceError:错误#1069:在String上找不到属性，并且没有默认值

我正在使用URLRequest在flash中加载一个外部php文件。但不幸的是，我得到了这个错误-

ReferenceError: Error #1069:Property email not found on String and there is no default value.
    at Main/variablesGot()
    at flash.events::EventDispatcher/dispatchEventFunction()
    at flash.events::EventDispatcher/dispatchEvent()
    at flash.net::URLLoader/onComplete()

这是相关的as3代码

phpLoader.addEventListener(Event.COMPLETE, variablesGot);    
private function variablesGot(ev:Event):void
    {
        trace(ev.target.data.toString());  //THIS OUTPUTS CORRECTLY
        //OUTPUT for this trace is as follows
        //athleteName=ankur&email=email@yahoo.com&password=newpass&personalBest=9.58&shirtNumber=10         
        trace(ev.target.data.email.toString()); //LINE WITH ERROR
    }

以下是我正在加载的php文件中的相关php代码

print "athleteName=".$_SESSION[athleteName];
print "&email=".$_SESSION[email];
print "&password=".$_SESSION[password];
print "&personalBest=".$_SESSION[personalBest];
print "&shirtNumber=".$_SESSION[shirtNumber];
print "&country=".$_SESSION[country];

我想这个错误可能是由于我在php中打印的方式造成的？但我不确定。