[flexcoders] missing results in datagrid

[vr6stress]

[newbie]
it seems fairly straight forward, i use the httpservice to call a url
with a couple of requests. i get the result and can display the raw
data. but when i try to put it in a datagrid i get nothing. of course
i get cannot bind errors - but i have another test to a different feed
that works just fine.

xml response from url (there are other items but i'm only concerned
with these 3)
<accountCoupon>
<accountCouponRow>
<BAR_CODE_NUMBER>001260429006210705</BAR_CODE_NUMBER>
<COUPON_VALUE>5</COUPON_VALUE>
<EXP_DATE>2009-03-29T00:00:00-06:00</EXP_DATE>
</accountCouponRow>
</accountCoupon>

application
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml";
layout="absolute" backgroundColor="#f6f6f6"
backgroundGradientColors="[#f6f6f6, #bbbbbb]">

   <mx:Label x="10" y="10" text="Submit form using post method"
fontSize="20" fontWeight="bold"/>
   <mx:HRule x="10" y="49" width="80%"/>
   
   <mx:Script>
      <![CDATA[
        import mx.utils.ObjectProxy;
         import mx.rpc.events.FaultEvent;
         import mx.rpc.events.ResultEvent;
         import mx.utils.ArrayUtil;
         
         [Bindable]
         public function handleResult(event:ResultEvent):void {
                
            textarea1.text = "Response from HTTPService call:\n " +
String(event.result);
         }
         public function handleFault(event:FaultEvent):void {
            textarea1.text = "Fault Response from HTTPService call:\n
" + event.fault.toString();
         }
         
      ]]>
   </mx:Script>

   <mx:HTTPService id="form1" showBusyCursor="true"
url="http://sorry.can't.show.url"
                method="POST" 
                result="handleResult(event)" 
                fault="handleFault(event)" resultFormat="e4x">
      <mx:request>
         <card_number>{bar_code.text}</card_number>
         <zipcode>{zip_code.text}</zipcode>
      </mx:request>
   </mx:HTTPService>



<!-- Visual Items -->
   <mx:Label x="10" y="139" text="Result"/>
   <mx:TextArea x="10" y="165" width="470" height="188" id="textarea1"/>
   <mx:TextInput id="bar_code" x="10" y="71" text="000000624586"/>
   <mx:TextInput id="zip_code" text="84403" x="10" y="101"/>
   <mx:Button x="178" y="71" label="Submit" click="form1.send()"/>
   <mx:DataGrid x="10" y="361" width="470" height="318"
id="showCoupons"
dataProvider="{form1.lastResult.accountCoupon.accountCouponRow}">
      <mx:columns>
         <mx:DataGridColumn headerText="Coupon"
dataField="BAR_CODE_NUMBER"/>
         <mx:DataGridColumn headerText="Exp Date" dataField="EXP_DATE"/>
         <mx:DataGridColumn headerText="Value" dataField="COUPON_VALUE"/>
      </mx:columns>
   </mx:DataGrid>

</mx:Application>

granted this application has been hacked together, but i'd still like
to know where i'm going wrong...my other application reading a feed
works perfectly and is basically the same when it comes to displaying
the xml in the datagrid...

help