InventoryOnhand AIF Question (Ax2009 AP1)

im getting folowing error when i call READ method of Inventoryonhand AIF service 

"itemid is not a field in data source inventsum"

iam using SOAP Ui and below is the request . I have tried Inventdimid also as it is one of index fields.,

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://schemas.microsoft.com/dynamics/2008/01/services" xmlns:quer="http://schemas.microsoft.com/dynamics/2006/02/documents/QueryCriteria">

   <soapenv:Header/>

   <soapenv:Body>

      <ser:InventoryOnHandService_basicFindKeysRequest>

         <!--Optional:-->

         <quer:QueryCriteria>

            <quer:CriteriaElement>

               <quer:DataSourceName>inventsum</quer:DataSourceName>

               <quer:FieldName>itemid</quer:FieldName>

               <quer:Operator>EQUAL</quer:Operator>

               <quer:Value1>02113001429</quer:Value1>

            </quer:CriteriaElement>

         </quer:QueryCriteria>

      </ser:InventoryOnHandService_basicFindKeysRequest>

   </soapenv:Body>

</soapenv:Envelope>

Please help