Web Service receives Blank values when sent through SOAP

Hi,
I am succefully able to envoke a web method using SOAP toolkit v3.0, but parameters passed to web service are received as blank.

Please suggest.

Note: fromNavision is a webmethod and it returns string.
SOAP Code

IF ISCLEAR(Connector) THEN
CREATE(Connector);

//Connector.Property(‘ProxyServer’,‘isaserver’);
//Connector.Property(‘ProxyPassword’,‘proxypass’);
//Connector.Property(‘ProxyUser’,‘username’);
Connector.Property(‘EndPointURL’,‘http://localhost:1484/MCC-Webservice/Service.asmx?WSDL’);
Connector.Connect;
Connector.Property(‘SoapAction’,‘http://tempuri.org/fromNavision’);
Connector.BeginMessage;

CREATE(Serializer);
Serializer.Init(Connector.InputStream);
Serializer.StartEnvelope(’’,‘STANDARD’,‘utf-8’);
Serializer.StartBody(‘STANDARD’);
Serializer.StartElement(‘BillingService’,‘uri:fromNavision’);
Serializer.WriteString(‘Testing’);
Serializer.EndElement;
Serializer.EndBody;
Serializer.EndEnvelope;
Connector.EndMessage;
CLEAR(Connector);

And my web method is,

[WebMethod]
public string fromNavision(string messageString)
{
string testData = “Test”;
logger.Debug("Obtained Request: " + messageString);
return testData;
}

in above code, messageString is coming as null. and I am using SOAP Toolkit v3.0 in Navision.
Please suggest

Thanks & Regards,

Vikas