Soap Client not working

[Carlos Alegria Galicia]

Hi,

I am using Zend v2.5.1 I am getting the following error while trying to use
Soap Client:

System.Web.Services.Protocols.SoapException: Server was unable to
process request. ---> System.NullReferenceException: Object reference
not set to an instance of an object.

I am creating the client with the following code:

---
$this->soapClient = new Client(
        "file://" . __DIR__ . "/a_file.wsdl",
        array(
        'soap_version' => SOAP_1_2
        ));

$this->soapClient->MethdName("string argument");
---


Any help or insight about this issue will be appreciated,
Carlos Alegría