Problem with SOAP

[mikaint]

I'm trying to authenticate a user using soap but i get an error and i don't really know what's wrong...

getFunctions will return

array(1) { [0]=> string(59) "authenticateResponse authenticate(authenticate $parameters)" } 

I don't know if my code is correct, but anyway my code is:

$client = new SoapClient('....../file?wsdl');
echo $result = $client->__SoapCall('authenticate',array("username" => "test", "password" => sha1("test")));

The above will return

Fatal error: Uncaught SoapFault exception: [s:Server] id to load is required for loading in D:\wamp\www\test.php:54 Stack trace: #0 D:\wamp\www\test.php(54): SoapClient->__soapCall('authenticate', Array) #1 {main} thrown in D:\wamp\www\test.php on line 54

Any advices would be REEEALLY helpful! Thanks