c# webservice从php调用返回null

我正在调用一个web服务(c#)，它使用nusoap_client从php代码生成(1到5)之间的随机数。php代码如下

$client = new nusoap_client('http://localhost/TestWebService/TestWebService.asmx?WSDL','TRUE');
//echo("execute". $client);
$result = $client->call('GenerateRandomNumber');
//echo("executerandomn".$result);
$return=redirectpage($result); //redirectpage() function redirects the user based on the random number generated.

函数GenerateRandomNumber()返回null。我试着单独浏览web服务，它的工作，但不是通过php调用。

创建的WSDL在

下面

<?xml version="1.0" encoding="utf-8"?>
<wsdl:definitions xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"   xmlns:tm="http://microsoft.com/wsdl/mime/textMatching/"   xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/" xmlns:tns="http://tempuri.org/" xmlns:s="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://schemas.xmlsoap.org/wsdl/soap12/" xmlns:http="http://schemas.xmlsoap.org/wsdl/http/" targetNamespace="http://tempuri.org/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">
<wsdl:types>
<s:schema elementFormDefault="qualified" targetNamespace="http://tempuri.org/">
<s:element name="GenerateRandomNumber">
<s:complexType />
</s:element>
<s:element name="GenerateRandomNumberResponse">
<s:complexType>
<s:sequence>
<s:element minOccurs="1" maxOccurs="1" name="GenerateRandomNumberResult" type="s:int" />
      </s:sequence>
    </s:complexType>
  </s:element>
</s:schema>
</wsdl:types>
<wsdl:message name="GenerateRandomNumberSoapIn">
<wsdl:part name="parameters" element="tns:GenerateRandomNumber" />
</wsdl:message>
<wsdl:message name="GenerateRandomNumberSoapOut">
<wsdl:part name="parameters" element="tns:GenerateRandomNumberResponse" />
</wsdl:message>
<wsdl:portType name="TestWebServiceSoap">
<wsdl:operation name="GenerateRandomNumber">
  <wsdl:input message="tns:GenerateRandomNumberSoapIn" />
  <wsdl:output message="tns:GenerateRandomNumberSoapOut" />
  </wsdl:operation>
        </wsdl:portType>
 <wsdl:binding name="TestWebServiceSoap" type="tns:TestWebServiceSoap">
  <soap:binding transport="http://schemas.xmlsoap.org/soap/http" />
  <wsdl:operation name="GenerateRandomNumber">
  <soap:operation soapAction="http://tempuri.org/GenerateRandomNumber" style="document" />
  <wsdl:input>
    <soap:body use="literal" />
    </wsdl:input>
    <wsdl:output>
    <soap:body use="literal" />
    </wsdl:output>
    </wsdl:operation>
    </wsdl:binding>
    <wsdl:binding name="TestWebServiceSoap12" type="tns:TestWebServiceSoap">
    <soap12:binding transport="http://schemas.xmlsoap.org/soap/http" />
    <wsdl:operation name="GenerateRandomNumber">
    <soap12:operation soapAction="http://tempuri.org/GenerateRandomNumber"  style="document" />
   <wsdl:input>
    <soap12:body use="literal" />
    </wsdl:input>
    <wsdl:output>
    <soap12:body use="literal" />
    </wsdl:output>
    </wsdl:operation>
    </wsdl:binding>
    <wsdl:service name="TestWebService">
    <wsdl:port name="TestWebServiceSoap" binding="tns:TestWebServiceSoap">
     <soap:address location="http://localhost/TestWebService/TestWebService.asmx" />
      </wsdl:port>
      <wsdl:port name="TestWebServiceSoap12" binding="tns:TestWebServiceSoap12">
     <soap12:address location="http://localhost/TestWebService/TestWebService.asmx" />
     </wsdl:port>
     </wsdl:service>
     </wsdl:definitions>

请帮。