Web services

Ive been trying to upload users via web service using core_users_create_users but I can't upload more than one custom field any suggestions please? 

This works but when I add another custom field I get an error:

<soapenv:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://xxxxxx/p/webservice/soap/server.php?wstoken=786469bd0ea7e012c8bdc93xxxx7a5f">

   <soapenv:Header/>

   <soapenv:Body>

      <ser:core_user_create_users soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">

         <users xsi:type="soapenc:Array" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/">

             <Item soapenc:id="id1">

               <username xsi:type="xsd:string">gokusaiyaseis</username>

               <password xsi:type="xsd:string">Description_1.</password>

               <firstname xsi:type="xsd:string">Juan</firstname>

               <lastname xsi:type="xsd:string">Perez</lastname>

               <email xsi:type="xsd:string">gokurocksseis@example.com</email>

               <auth xsi:type="xsd:string">manual</auth>

               <customfields xsi:type="xsd:list">

                <customfields>

              <type xsi:type="xds:string">idasociado</type>

              <value xsi:type="xds:string">1285678</value>

                </customfields>

               </customfields>

            </Item>

         </users>

      </ser:core_user_create_users>

   </soapenv:Body>

</soapenv:Envelope>