jQuery Grid Plugin - jqGrid

I have this jqgrid trying to do multiselect. When i click my button that gets the selected rows and just puts them to an alert, all it says is "null"

can anyone help?

  <script type="text/javascript">
                var d = new Date();
                var month = d.getMonth() + 1;
                var date = d.getDate().toString();
                var year = d.getFullYear().toString();
                var gridUr = '<%=ResolveUrl("~/DealerServices/JsonScheduledSpas" )%>';
                var themeURL = '<%=AppHelper.themeImageUrl() %>';
                //var themeURL = '../../../../Content/Themes/EggPlant/Images/';
                var newQuerydate;

               
                jQuery("#ScheduledList").jqGrid({
                    
                    url: gridUr + '/' + month + '/' + date + '/' + year,
                    datatype: 'json',
                    mtype: 'GET',
                    altRows: 'true',
                    colNames: ['Invoice', 'Status', 'Company', 'Contact', 'Model', 'Customer', 'Order Notes', 'Internal Notes', 'DSR', 'Prod Date'],
                    colModel: [
                         { name: 'invoice', index: 'id', width: 50, align: 'left' },
                         { name: 'orderStatus', index: 'orderStatus', width: 50, align: 'left' },
                         { name: 'company', index: 'company', width: 200, align: 'left' },
                         { name: 'companyContactNumber', index: 'companyContactNumber', width: 100, align: 'left' },
                         { name: 'descript', index: 'descript', width: 60, align: 'left' },
                         { name: 'CustomerName', index: 'CustomerName', width: 100, align: 'left' },
                         { name: 'orderNotes', index: 'orderNotes', width: 125, align: 'left' },
                         { name: 'internalNotes', index: 'internalNotes', width: 175, align: 'left' },
                         { name: 'DsrFirstName', index: 'DsrFirstName', width: 70, align: 'left' },
                         { name: 'ProductionDate', index: 'ProductionDate', width: 60, align: 'left' }

                           ],
                    pager: jQuery('#Scheduledpager'),
                    rowNum: 20,
                    rowList: [5, 10, 20, 50],
                    sortname: 'Id',
                    sortorder: "desc",
                    viewrecords: true,
                    height: '300px',
                    width: '1000px',
                    multiselect:true
                  
                }); //end jQuery("#ScheduledList").jqGrid

 $("#release").button().click(function() {
                    var selected;
                    selected = jQuery("#ScheduledList").jqGrid('getGridParam', 'selarrow');
                    alert(selected);
                });