Estou tentando implementar um serviço da Web em execução em um sistema SAP PI. O WSDL que eu tenho é assim:

<?xml version="1.0" encoding="UTF-8"?>
<wsdl:definitions name="request_SO" targetNamespace="http://company.ch/orstest/jason_test" xmlns:p1="http://company.ch/orstest/jason_test" xmlns:wsp="http://schemas.xmlsoap.org/ws/2004/09/policy" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">
    <wsdl:documentation/>
    <wsp:UsingPolicy wsdl:required="true"/>
    <wsp:Policy wsu:Id="OP_request_SO"/>
    <wsdl:types>
        <xsd:schema targetNamespace="http://company.ch/orstest/jason_test" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://company.ch/orstest/jason_test">
            <xsd:element name="request" type="request"/>
            <xsd:element name="response" type="response"/>
            <xsd:complexType name="request">
                <xsd:annotation>
                    <xsd:appinfo source="http://sap.com/xi/VersionID">a8b7948ac2e211e2b2380000001f0d6a</xsd:appinfo>
                </xsd:annotation>
                <xsd:sequence>
                    <xsd:element name="body" type="xsd:string"/>
                </xsd:sequence>
            </xsd:complexType>
            <xsd:complexType name="response">
                <xsd:annotation>
                    <xsd:appinfo source="http://sap.com/xi/VersionID">bf49af09c36c11e299790000001f0d6a</xsd:appinfo>
                </xsd:annotation>
                <xsd:sequence>
                    <xsd:element name="body" type="xsd:string"/>
                </xsd:sequence>
            </xsd:complexType>
        </xsd:schema>
    </wsdl:types>
    <wsdl:message name="request">
        <wsdl:documentation/>
        <wsdl:part name="request" element="p1:request"/>
    </wsdl:message>
    <wsdl:message name="response">
        <wsdl:documentation/>
        <wsdl:part name="response" element="p1:response"/>
    </wsdl:message>
    <wsdl:portType name="request_SO">
        <wsdl:documentation/>
        <wsdl:operation name="request_SO">
            <wsdl:documentation/>
            <wsp:Policy>
                <wsp:PolicyReference URI="#OP_request_SO"/>
            </wsp:Policy>
            <wsdl:input message="p1:request"/>
            <wsdl:output message="p1:response"/>
        </wsdl:operation>
    </wsdl:portType>
    <wsdl:binding name="request_SOBinding" type="p1:request_SO">
        <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"/>
        <wsdl:operation name="request_SO">
            <soap:operation soapAction="http://sap.com/xi/WebService/soap1.1" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"/>
            <wsdl:input>
                <soap:body use="literal" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"/>
            </wsdl:input>
            <wsdl:output>
                <soap:body use="literal" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"/>
            </wsdl:output>
        </wsdl:operation>
    </wsdl:binding>
    <wsdl:service name="request_SOService">
        <wsdl:port name="HTTP_Port" binding="p1:request_SOBinding">
            <soap:address location="http://qa1100ap601.company.car.web:50000/XISOAPAdapter/MessageServlet?senderParty=&amp;senderService=BS_ORS&amp;receiverParty=&amp;receiverService=&amp;interface=request_SO&amp;interfaceNamespace=http://company.ch/orstest/jason_test" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"/>
        </wsdl:port>
        <wsdl:port name="HTTPS_Port" binding="p1:request_SOBinding">
            <soap:address location="https://qas.soa.subcompany.company.ch/XISOAPAdapter/MessageServlet?senderParty=&amp;senderService=BS_ORS&amp;receiverParty=&amp;receiverService=&amp;interface=request_SO&amp;interfaceNamespace=http://company.ch/orstest/jason_test" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"/>
        </wsdl:port>
    </wsdl:service>
</wsdl:definitions>

Meu arquivo PHP se parece com isso (nada mais nele atualmente):

<?php 
$client = new SoapClient('test.wsdl');
?> 

Quando estou executando meu script, recebo o seguinte erro:

Fatal error: Uncaught SoapFault exception: [WSDL] SOAP-ERROR: Parsing WSDL: Unknown required WSDL extension 'http://schemas.xmlsoap.org/ws/2004/09/policy' in /srv/www/htdocs/wsdl.php:2 Stack trace: #0 /srv/www/htdocs/wsdl.php(2): SoapClient->SoapClient('test.wsdl') #1 {main} thrown in /srv/www/htdocs/wsdl.php on line 2

Eu tentei procurar o erro no google e StackOverflow, e também verifiquei os comentários no php.net, mas não consigo descobrir o que eu teria que mudar a fim de obter este serviço em execução. Eu também tentei abrir o URL da extensão WSDL, parece existir.

Alguém pode me atirar um osso aqui? Tentei remover o URL de extensão, o que resulta no seguinte erro:

Fatal error: Uncaught SoapFault exception: [WSDL] SOAP-ERROR: Parsing WSDL: Unexpected WSDL element <UsingPolicy> in /srv/www/htdocs/wsdl.php:2 Stack trace: #0 /srv/www/htdocs/wsdl.php(2): SoapClient->SoapClient('test.wsdl') #1 {main} thrown in /srv/www/htdocs/wsdl.php on line 2