Java.lang.NullPointerException when calling java web service from .net

Question

I use the java web service from the .NET web application and get the mentioned exception "java.lang.NullPointerException", the type of .NET exception is Sysem.ServiceModel.FaultException. I do not have access to the web service code

Web service call:

var response = tere.agregarGuia( guia );

Corresponding wsdl:

<xs:complexType name="agregarGuia">
    <xs:sequence>
    <xs:element minOccurs="0" name="guia" type="xs:string"/>
    <xs:element minOccurs="0" name="autenticacion" type="tns:autenticacion"/>
    </xs:sequence>
</xs:complexType>
<xs:complexType name="autenticacion">
    <xs:sequence>
    <xs:element minOccurs="0" name="codAduana" type="xs:string"/>
    <xs:element minOccurs="0" name="firmaWSAA" type="xs:string"/>
    <xs:element minOccurs="0" name="idUsuario" type="xs:string"/>
    <xs:element minOccurs="0" name="ticketWSAA" type="xs:string"/></xs:sequence></xs:complexType>
.....
<operation name="agregarGuia" parameterOrder="agregarGuia">
    <input message="tns:serviciotereSoap_agregarGuia"/>
    <output message="tns:serviciotereSoap_agregarGuiaResponse"/>
</operation>

What could be the problem? Is there a tool that allows me to get more out of running a web service?