jQuery Grid Plugin - jqGrid

Hi. I almost finish my grid code but the navigation button keep "disabled" altough i have more data to show.
My grid definition is
   jQuery("#list").jqGrid({
            caption: 'Sectores',
            colNames:['Codigo','Nombre'],
            colModel :[
              { name: "co_sector", index: "co_sector", width: 20, editable: true, search: false },
              { name: "nb_sector", index: "nb_sector", width: 90, editable: true, editoptions: {size: "60", maxlength: "60"}, editrules:{requerided:true}}
            ],
            datatype: "json",
            editurl: urlString,
            hidegrid: false,
            height: "47%",
            imgpath: "../js/themes/basic/images",
            jsonReader: {
        repeatitems : true,
        id: "0"
            },
            loadtext: "Cargando...",
            loadui: "block",
            mtype: "GET",
            pager: jQuery('#pager'),
            recordtext: "Registros en total.",
            rowNum: 10,
            sortname: "nb_sector",
            sortorder: "asc",
            toolbar: [true, "bottom"],
            url: urlString,
            viewrecords: true,
            width : 800,
            loadError : function(xhr,st,err) {
                jQuery("#rsperror").html("Type: "+st+"; Response: "+ xhr.status + " "+xhr.statusText);
            }            
         }).navGrid("#pager",
            {}, //options
            { height:100, width:500,
              reloadAfterSubmit:false
            }, // edit options
            { height:280,width:300,  reloadAfterSubmit:true  }, // add options
            { height:90, width:300,  reloadAfterSubmit:false,
              beforeSubmit: function() {
                 var sr = jQuery("#list").getGridParam('selrow');
                 var rowData = jQuery("#list").getRowData(sr);
           
                  this.delData = {"co_sector" : rowData['co_sector']};
                  retarr = {"co_sector" : rowData['co_sector']};
                  return retarr;
              }
            }, // del options
            {} // search options      
            ).navButtonAdd("#pager", {
                caption: "",
                buttonimg: "../images/page_excel.png",
                onClickButton: function() {
                    showReportWindow("excel");
                },
                position: "last"
            }).navButtonAdd("#pager", {
                caption: "",
                buttonimg: "../images/page_white_acrobat.png",
                onClickButton: function() {
                    showReportWindow("pdf");
                },
                position: "last"
         });   

         
And my json response is

{ total: "1",
  page: "1",
  records: "19",
  rows :[{id: "1", cell:["11","ADMISTRACIÓN LEGAL Y FINANZAS"]},
         {id: "2", cell:["4","ASEGURADORA, ARREDADORA FINANCIERA Y OTROS AFINES"]},
         {id: "3", cell:["16","CAJA DE AHORRO, COOPERATIVA O AFINES"]},
         {id: "4", cell:["10","CENTROS EDUCATIVOS Y AFINES"]},
         {id: "5",cell:["2","COMERCIALIZADORA DE PRODUCTOS ELECTRÓDOMESTICOS, COMPUTACIÓN, MAN"]},
         {id: "6",cell:["1","EDITORIAL, VENTA DE LIBROS (MAYOR O DETAL) Y AFINES"]},
         {id: "7",cell:["14","EMPRESAS DE CONSULTORÍA, DESARROLLO DE SOFTWARE Y AFINES"]},
         {id: "8",cell:["17","EMPRESAS DE SERVICIOS EN GENERAL"]},
         {id: "9",cell:["15","FUNDACIÓN SIN FINES DE LUCRO"]},
         {id: "10",cell:["9","INMOBILIARIAS, ADMINISTRADORAS DE BIENES RAÍCES Y AFINES"]}
     ]
}

Is there somethig I left out ?