Soap connection problem

[goodmast3r]

I'm having a problem using SOAP. It is accessing http://uat.webservice.apm.com.au/fee...tial.asmx?WSDL

My code is :

    $client = new SoapClient("http://uat.webservice.apm.com.au/feed/residential.asmx?WSDL");

    $params = array('login' =>'theusername',
                    'password' =>'thepassword',
                    'trace' => 1,
                    'postcode' =>'2112',
                    'state' => 'nsw'
                    );

    $result = $client->GetResidentialResultsByPostcodeState($params); 

The error is "System.Web.Services.Protocols.SoapHeaderException: Invalid Username/Password at Residential.GetResidentialResultsByPostcodeState(String postcode, String state". I've checked the username and password, it's correct. But I have doubt on my code. Anything wrong with it? Thanks.