Sopa Service Erro

[Ifahad]

Hi,
i AM TRYING TO WRITE MY FIRST SOAP CLIENT IN PHP. wHEN i TRY TO ACCESS A SERVICE I GOT FOLLOWING ERROR.

Server was unable to process request. ---> Object reference not set to an instance of an object

tHE COE i AM USING IS

class Test {
    public $ordno;
    }
$parameters = new Test;
$parameters -> ordno = "SOR01212";

$client = new SoapClient ("MYSERVER.DSL");
$client -> CancelOrder($parameters);

PLEASE HELP ME I CAN FIGURE OUT THE PROBLEM.
THANKS