the server responded with a status of 500 (Internal Server Error)

$(document).ready(function () {
    $.jgrid.formatter.integer.thousandsSeparator = ',';
    $.jgrid.formatter.number.thousandsSeparator = ',';
    $.jgrid.formatter.currency.thousandsSeparator = ',';

    $('#list').jqGrid({
        caption: "رسته نان",
        //url from wich data should be requested
        url: '@Url.Action("Gettemps", "TypeBread")',
        //url for edit operation
        editurl: '@Url.Action("Edittemp", "TypeBread")',
        //type of data
        datatype: 'json',
        jsonReader: {
            root: "Rows",
            page: "Page",
            total: "Total",
            records: "Records",
            repeatitems: true,
            userdata: "UserData",
            id: "ID_Baker",
            cell: "RowCells"
        },
        //url access method type
        mtype: 'POST',
        //columns names
        colNames: [' نام رسته ', 'شماره', ' '],
        //columns model
        colModel: [
            {
                name: '@(StronglyTyped.PropertyName<typebaker>(x => x.FNameTypeBaker))',
                index: '@(StronglyTyped.PropertyName<typebaker>(x => x.FNameTypeBaker))',
                align: 'right', width: 400,
                editable: true, edittype: 'text', hidden: false,
                editoptions: {
                    maxlength: 100
                },
                editrules: {
                    required: true
                }
            },
            {
                name: '@(StronglyTyped.PropertyName<typebaker>(x=>x.ID_Baker))',
                index: '@(StronglyTyped.PropertyName<typebaker>(x => x.ID_Baker))',
                align: 'right', width: 170,
                editable: false, hidden: true, key: true
            },
            {
                name: 'myac', width: 80, fixed: true, sortable: false,
                resize: false, formatter: 'actions',
                formatoptions: {
                    keys: true,
                    delbutton: true,
                    delOptions: {
                        url: '@Url.Action("Deletetemp", "TypeBread")',

                    }

            }
            }
        ],
        //pager for grid
        pager: $('#pager'),
        //number of rows per page
        rowNum: 10,
        rowList: [10, 20, 50, 100],
        //initial sorting column
        sortname: 'ID_Baker',
        //initial sorting direction
        sortorder: 'asc',
        //we want to display total records count
        viewrecords: true,
        width: '800',
        shrinkToFit: false,
        height: 'auto',
        hidegrid: false,
        direction: "rtl",
        gridview: true,
        rownumbers: true,
        loadComplete: function () {
            //change alternate rows color
            $("tr.jqgrow:odd").css("background", "#E0E0E0");
        },
        loadError: function (xhr, st, err) {
            jQuery("#rsperror").html("Type: " + st + "; Response: " + xhr.status + " " + xhr.statusText);
        },
        multiselect: true
    }).jqGrid('gridResize', { minWidth: 400 });
});

var lastSel;
function inlineEdit() {
    $('input[name=rdEditApproach]').attr('disabled', true);
    $('#list').navGrid(
        '#pager',
        //enabling buttons
        { add: true, del: true, edit: false, search: false },
        //edit options
        {},
        //add options
        { width: 'auto', url: '@Url.Action("Addtemp", "TypeBread")' },
    //delete options
        { url: '@Url.Action("Deletetemp", "TypeBread")' }
);
    //add onSelectRow event to support inline edit
    $('#list').setGridParam({
        onSelectRow: function (id) {
            if (id && id != lastSel) {
                //save changes in row
                $('#list').saveRow(lastSel, false);
                lastSel = id;
            }
            //trigger inline edit for row
            $('#list').editRow(id, true);
        }
    });
};

function formEdit() {
    $('input[name=rdEditApproach]').attr('disabled', true);
    $('#list').navGrid(
            '#pager',
            //enabling buttons
            { add: true, del: true, edit: true, search: false },
            //edit option
            {
                width: 'auto', checkOnUpdate: true, checkOnSubmit: true,
                beforeShowForm: function (form) {
                    centerDialog(form, $('#list'));
                }
            },
            //add options
            {
                width: 'auto', url: '@Url.Action("Addtemp", "TypeBread")',
                reloadAfterSubmit: true, checkOnUpdate: true, checkOnSubmit: true,
                beforeShowForm: function (form) {
                    centerDialog(form, $('#list'));
                }
            },
            //delete options
            {
                url: '@Url.Action("Deletetemp", "TypeBread")', reloadAfterSubmit: true
            })
        //.jqGrid('navButtonAdd', "#pager", {
          //  caption: "حذف ردیف‌های انتخابی", title: "Delete Toolbar", buttonicon: 'ui-icon ui-icon-trash',
          //  onClickButton: function () {
           //     var idsList = jQuery("#list").jqGrid('getGridParam', 'selarrrow');
           //     alert(idsList);
                //jQuery("#list").jqGrid('delGridRow',idsList,{reloadAfterSubmit:false});
          //  }
        //});
};

function centerDialog(form, grid) {
    var dlgDiv = $("#editmod" + grid[0].id);
    var parentDiv = dlgDiv.parent(); // div#gbox_list
    var dlgWidth = dlgDiv.width();
    var parentWidth = parentDiv.width();
    var dlgHeight = dlgDiv.height();
    var parentHeight = parentDiv.height();
    var parentTop = parentDiv.offset().top;
    var parentLeft = parentDiv.offset().left;
    dlgDiv[0].style.top = Math.round(parentTop + (parentHeight - dlgHeight) / 2) + "px";
    dlgDiv[0].style.left = Math.round(parentLeft + (parentWidth - dlgWidth) / 2) + "px";
}

[HttpPost]
          public ActionResult Addtemp(typebaker postData)
          {
              Classtypebaker _Classbaker = new Classtypebaker();
              //todo: Add temp to repository
              if (postData == null)
                  return Json(false);
              int baker = _Classbaker.checkbaker(postData.FNameTypeBaker);
              if (baker <= 0)
            {
                db.typebakers.Add(postData);
                db.SaveChanges();
                return Json(true);
            }
              else
              {

                  ViewBag.Name = "this dublicate record";
                  return View(ViewBag.Name);
                //  return Json(true);
              }
            ///  return Json(true);
          }