get error with using php nusoap for web service

i want get data from a webserver (.net) and display it into my website.

my code is :

$cli开发者_运维技巧ent = new soapclient('http://www.tsetmc.com/WebService/TsePublic.asmx?WSDL', true);
$client->useHTTPPersistentConnection(); 

$user = array('UserName' => 'etc');
$pass = array('Password' => 'etc');

$result = $client->call('Board', $user, $pass);

print_r( $result );

and i get this error :

Warning: Illegal offset type in isset or empty in /home/mmdicir/public_html/lib/nusoap-0.7.3/lib/nusoap.php on line 7211

Array ( [faultcode] => soap:Server [faultstring] => Server was unable to process request. ---> String reference not set to an instance of a String. Parameter name: s [detail] => )

$client = new soapclient('http://www.tsetmc.com/WebService/TsePublic.asmx?WSDL', true);
$client->useHTTPPersistentConnection(); 

$user = array('UserName' => 'etc', 'Password' => 'etc'); use like this its will work
//$pass = array('Password' => 'etc'); // wrong

$result = $client->call('Board', $user, $pass);

print_r( $result );