Calling .NET Web Service using nuSOAP

Hi all

I have developed a .NET Web Service that require a Username and Password be sent in the SOAP Header. The SOAP Header is a class in the Web Service called "AuthenticationHeader".
The problem occurs when a PHP Client using nuSOAP wants to call the Web Service, the user is not authenticated. I am not a PHP fundi, but the code that PHP developer sent me don't seem to send the credentials at the right time. I might be wrong, that's why I ask for help. Here's he's code:

require_once("lib/nusoap.php");
$wsdl=("http://WEBSERVICE_ADDRESS?wsdl";
$client= new soapclient($wsdl,'wsdl', true);
$param7='getClass';
$userName='me';
$passWord='pass';
$client->username = $userName;
$client->password = $passWord;
$client->setCredentials($userName,$passWord);
$client->debug_flag=1;
$var= $client->call($param7);
$err = $client->getError();

This is urgent, your help will be highly appreciated.

Regards
walterd