Sessions/Cookies with WSClient in WSDL Mode

Hello, I am trying to find out if there is a way to retain session cookies when using WSClient (specifically in WSDL mode). I connect to a vendor's web service that uses a session-based authentication method. Unfortunately, even though my initial login() method call is successful, any other methods I call throw an exception because the information it needs is not available in the session. I am able to get this working using the built-in PHP SOAP functions, but I need to make some calls that depend on file attachments, which was why I was hoping WSF/PHP could do what I needed. Any suggestions would be appreciated! Below is the an example of what I'm trying to do: ------ $login_parameters = array( 'username' => MYUSER, 'password' => MYPASS ); $client = new WSClient( array( "wsdl" => "http://ws1.responsys.net/webservices/ResponsysWS?WSDL", "to" => "http://ws1.responsys.net/webservices/ResponsysWS", )); $proxy = $client->getProxy(); $proxy->login( $login_parameters ); $proxy->listFolders(); ------ The login() call returns true, but the listFolders() method throws an exception: Fatal error: Uncaught WS FAULT exception: [soapenv:Server.userException] java.rmi.RemoteException: RIAccount object is not available in session