javax.xml.ws.WebServiceException: Unexpected response element ,,, error

Sometimes, you get javax.xml.ws.WebServiceException: Unexpected response element ,,, error while running a bpel process from a client. 

The error is well defined here: http://forums.netbeans.org/topic11185.html

One way to get rid of this error is adding namespace attribute to the operation definition in the wsdl of the bpel process as follows:

 <binding name="calculatorMtomWSDLPortTypeBinding" type="tns:calculatorMtomWSDLPortType">

        <soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/>

        <operation name="calculatorMtomWSDLOperation">

            <soap:operation/>

            <input name="input1">

                <soap:body use="literal" namespace="http://j2ee.netbeans.org/wsdl/CalculatorMtom/calculatorMtomWSDL"/>

            </input>

            <output name="output1">

                <soap:body use="literal" namespace="http://j2ee.netbeans.org/wsdl/CalculatorMtom/calculatorMtomWSDL"/>

            </output>

        </operation>

    </binding>

in short, lack of the red stuff above, leads the mentioned problem..