SAXException related to SimpleDeserializer

While sending a request, I am getting following error in response:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <soapenv:Body>
      <soapenv:Fault>
         <faultcode>soapenv:Server.userException</faultcode>
         <faultstring>org.xml.sax.SAXException: SimpleDeserializer encountered a child element, which is NOT expected, in something it was trying to deserialize.</faultstring>
         <detail>
            <ns1:hostname xmlns:ns1="http://xml.apache.org/axis/">whms11536</ns1:hostname>
         </detail>
      </soapenv:Fault>
   </soapenv:Body>
</soapenv:Envelope>

How can I resolve this error ?

Corresponding request is (note, for security reason, the endpoint address has been replaced with xxx.yyy.zzz)

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:reg="https://xxx.yyy.zzz/orc/services/RegisterClient">
  <soapenv:Header/>
   <soapenv:Body>
      <reg:registerRequest>
         <reg:request>
            <reg:businessName xsi:nil="true" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>
            <reg:businessOperatingName>Regresion One</reg:businessOperatingName>
            <reg:customerNumber>9219436</reg:customerNumber>
            <reg:marketingInfo>
               <reg:advertisingExpensePerYear>5000</reg:advertisingExpensePerYear>
               <reg:gender>F</reg:gender>
               <reg:homeBusiness>Y</reg:homeBusiness>
               <reg:numberOfEmployees>5</reg:numberOfEmployees>
               <reg:shippingExpensePerYear>600</reg:shippingExpensePerYear>
               <reg:shippingExpensePerYear2>?</reg:shippingExpensePerYear2>
               <reg:useOfCPCShippingLastYear>200</reg:useOfCPCShippingLastYear>
               <reg:yearsInOperation>10</reg:yearsInOperation>
               <reg:numberCardsRequired>1</reg:numberCardsRequired>
               <reg:rcNumber>V1</reg:rcNumber>
            </reg:marketingInfo>
            <reg:typeOfBusiness>Test</reg:typeOfBusiness>
            <reg:userInfo>
               <reg:address>
                  <reg:city>Ottawa</reg:city>
                  <reg:country>CA</reg:country>
                  <reg:postal_code>K2T1H5</reg:postal_code>
                  <reg:province>ON</reg:province>
                  <reg:street>57 Stikine Dr</reg:street>
                  <reg:street2>?</reg:street2>
               </reg:address>
               <reg:alternateMailingAddress>true</reg:alternateMailingAddress>
               <reg:communication>
                  <reg:email>regression.tester@test.com</reg:email>
                  <reg:emailReTyped>regression.tester@test.com</reg:emailReTyped>
                  <reg:fax>123-456-7890</reg:fax>
                  <reg:language>F</reg:language>
                  <reg:telephone>321-654-9876</reg:telephone>
               </reg:communication>
               <reg:firstname>Regression</reg:firstname>
               <reg:mailingAddress>
                  <reg:city>Ottawa</reg:city>
                  <reg:country>CA</reg:country>
                  <reg:postal_code>K2T1H5</reg:postal_code>
                  <reg:province>ON</reg:province>
                  <reg:street>57 Stikine Dr</reg:street>
                  <reg:street2>?</reg:street2>
               </reg:mailingAddress>
               <reg:title>Ms</reg:title>
            </reg:userInfo>
         </reg:request>
      </reg:registerRequest>
   </soapenv:Body>
</soapenv:Envelope>