Webservice in Python/soaplib anyone?

Hello,
has anyone managed to connect a Flex application to a Webservice implemented with soaplib, a Python webservice library? (http://trac.optio.webfactional.com/wiki/soaplib) The "Hello, World"-example is easy to setup and call from a Python script (http://trac.optio.webfactional.com/wiki/HelloWorld), but I fail to call the Webservice from Flex:

<?xml version="1.0"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
verticalGap="10">
<mx:Script>
<![CDATA[
import mx.controls.Alert;

public function onFault(fevent) : void {
trace("***", fevent);
Alert.show(fevent.fault.faultString, 'Error');
}

public function opResult(oevent) : void {
trace("###", oevent);
Alert.show(oevent.result, 'OK');
}
]]>
</mx:Script>


<!-- -->
<mx:WebService
id="helloWorldWS"
wsdl="http://localhost:7789/soap/api.wsdl"
useProxy="false"
result="strList=event.result"
fault="onFault(event)">
<mx:operation name="say_hello"
result="opResult(event)"
fault="onFault(event)">
<mx:request>
<tname>a</tname>
<times>2</times>
</mx:request>
</mx:operation>
</mx:WebService>
<!-- -->
<!--
<mx:WebService id="helloWorldWS"
wsdl="http://localhost:7789/soap/api.wsdl"
result="opResult(event)"
fault="onFault(event)">
<mx:operation name="say_hello"/>
</mx:WebService>
-->

<mx:Button label="Go!" click="helloWorldWS.say_hello.send()"/>
</mx:Application>

Hitting "Go!" leads to error: "Required parameter 'say_hello' not found in input arguments."

Has anyone an idea what is missing in the sample application?

TIA

Uwe