jquery dataTables warning: table id=IDtableU - Requested unknown parameter '0' for row 0

This is my first time using jquery dataTable pulg-in and I am facing an issue that I can't understand. I am using the server side configuration with JEE servlet. The problem that I get this error message: DataTables warning: table id=IDtableU - Requested unknown parameter '0' for row 0.
this is my dataTable initialisation:

$('#IDtableU').dataTable({
                                                "bServerSide": true, // use server side processing
                                                        "sAjaxSource": "/OCSReportingTool/updateuser",//the servlet
                                                        "bProcessing": true, // display processing message while fetching
                                                        "sPaginationType": "full_numbers",
                                                        "bJQueryUI": true,
                                                        //"aaData":
                                                                                                               [
                                                        { "type_U": "Account type" },
                                                                    { "SAMAccName_U": "User Name" },
                                                                    { "statusAD":"Status in AD"},
                                                                        { "statusDB":"Status in DB"},
                                                                        { "department":"Department"},
                                                                        { "cc":"Cost Center"},

                                                                    ]// mapping table coloumns with properties in json objects
                                                 });

HTML:
<table id=IDtableU>
       <thead>
              <tr>
                     <th>User Name </th>
                     <th>Account type </th>
                    <th>Department </th>
                    <th>Cost Center </th>
                    <th>Status in AD </th>
                    <th>Status in DB </th>
               </tr>
          </thead>
          <tbody>
          </tbody>
</table>

this JSON data sent back from the server (I used firebug to find the server response)

{"iTotalDisplayRecords":10,"iTotalRecords":6320,"aaData":[{"type_U":"local","SAMAccName_U":"NULL","statusAD":"incactive","statusDB":"incactive","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"t_de_ri","statusAD":"incactive","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"cbmr","statusAD":"incactive","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"a_grzanowskim","statusAD":"active","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"KuntzB","statusAD":"active","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"a_orglmeisterm","statusAD":"active","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"a_mauchg","statusAD":"active","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"WittelS","statusAD":"active","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"a_egloffm","statusAD":"active","statusDB":"active","department":"NULL","cc":0},{"type_U":"domain","SAMAccName_U":"a_noetzoldr","statusAD":"active","statusDB":"active","department":"NULL","cc":0}],"sEcho":1}

Datatables seems that it has parsed the result and it has successfully get "iTotalDisplayRecords' and 'iTotalRecords" but I get this error message:table id=IDtableU - Requested unknown parameter '0' for row 0 . Please I need your help, I have spent 2 days without fixing the problem it drives me crazy