[AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Edit(Nullable<int> id, FormCollection formValues)

Now it works.

I'm getting error Status: 'Internal Server Error'. Error code: 500. Edit seems to working fine as I hit my Controller breakpoint on the edir submit and all my formOptions are there. Here's my grid def. Thanks.

<script type="text/javascript">
    jQuery(document).ready(function() {
        jQuery("#sandgrid").jqGrid({
            url: '/EquipTrack/GridData/',
            editurl: '/EquipTrack/Edit/',
            datatype: 'json',
            mtype: 'GET',
            height: 255,
            width: 755,
            rowNum: 5000,
            colNames: ['ID', 'Type', 'Make', 'Model', 'Year', 'Location', 'Insp Due', 'Serv Due', 'Miles/Hrs', 'Milage Dt', 'Reg By', 'Mngd By', 'Tag Exp', '', '', '', '', 'Vin Num', 'Title Num', 'GVW', 'Unlaiden Wt', 'Tag Num', 'Tag State', 'Cost', 'Inspect Rmndr(wks)', 'Tag Rmndr(wks)', 'Stolen', 'Sold', 'Lojack', 'In Repair', 'Totaled', 'Hut Sticker', 'Apportioned', 'IFTA Sticker', 'Comment'],
            colModel: [
                   { name: 'equip_id', index: 'equip_id', width: 65, editable: true },
                  { name: 'type_desc', index: 'type_desc', width: 130, editable: true, edittype: "select", editoptions: { dataUrl: '/EquipTrack/GetTypes'} },
                   { name: 'make_descr', index: 'make_descr', width: 80, editable: true, edittype: "select", editoptions: { dataUrl: '/EquipTrack/GetMakes'} },
                   { name: 'model_descr', index: 'model_descr', width: 80, editable: true, edittype: "select", editoptions: { dataUrl: '/EquipTrack/GetModels'} },
                   { name: 'equip_year', index: 'equip_year', width: 60, editable: true },
                   { name: 'work_loc', index: 'work_loc', width: 130, editable: true },
                   { name: 'insp_due_dt', index: 'insp_due_dt', width: 100, editable: true },
                   { name: 'service_due_num', index: 'service_due_num', width: 80, editable: true },
                   { name: 'miles_hours', index: 'miles_hours', width: 80, editable: true },
                   { name: 'miles_dt', index: 'miles_dt', width: 100, editable: true },
                   { name: 'registered_by', index: 'registered_by', width: 80, editable: true, edittype: "select", editoptions: { dataUrl: '/EquipTrack/GetDivisions'} },
                   { name: 'managed_by', index: 'managed_by', width: 80, editable: true, edittype: "select", editoptions: { dataUrl: '/EquipTrack/GetDivisions'} },
                   { name: 'tag_expire_dt', index: 'tag_expire_dt', width: 100, editable: true,
                       editoptions: { size: 12, dataInit: function(el) {
                           $(el).datepicker({ dateFormat: 'mm/dd/yy' });
                       }
                       }
                   },
                   { name: 'inspection_warn', hidden: true },
                   { name: 'service_warn', hidden: true },
                   { name: 'tag_warn', hidden: true },
                   { name: 'equip_color', hidden: true },
                   { name: 'vin_num', hidden: true, editable: true, editrules: { edithidden: true} },
                   { name: 'title_num', hidden: true, editable: true, editrules: { edithidden: true} },
                { name: 'gross_v_wt', hidden: true, editable: true, editrules: { edithidden: true} },
            { name: 'unlaiden_wt', hidden: true, editable: true, editrules: { edithidden: true} },
            { name: 'tag_num', hidden: true, editable: true, editrules: { edithidden: true} },
            { name: 'tag_state', hidden: true, editable: true, editrules: { edithidden: true} },
            { name: 'cost', hidden: true, editable: true, editrules: { edithidden: true} },
                   { name: 'insp_rmdr_wks', hidden: true, editable: true, edittype: "select", editoptions: { value: ":;1:1;2:2;3:3;4:4;5:5;6:6;7:7;8:8;9:9;10:10;11:11;12:12;13:13;14:14;15:15;16:16;17:17;18:18;19:19;20:20;21:21;22:22;23:23;24:24" }, editrules: { edithidden: true} },
            { name: 'tag_expire_rmdr_wks', editable: true, hidden: true, edittype: "select", editoptions: { value: ":;1:1;2:2;3:3;4:4;5:5;6:6;7:7;8:8;9:9;10:10;11:11;12:12;13:13;14:14;15:15;16:16;17:17;18:18;19:19;20:20;21:21;22:22;23:23;24:24" }, editrules: { edithidden: true} },
            { name: 'stolen', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'sold', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'lojack', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'in_repair', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'totaled', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'hut_sticker', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'apportioned', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'ifta_sticker', hidden: true, editable: true, edittype: "checkbox", editoptions: { value: "True:False" }, editrules: { edithidden: true} },
            { name: 'comment', hidden: true, editable: true, editoptions: { value: "True:False" }, editrules: { edithidden: true }, edittype: "textarea", editoptions: { rows: "2", cols: "27"} }
],
            sortname: 'equip_id',
            sortorder: "asc",
            afterInsertRow: function(rowid, rowdata, rowelem) {
                if (rowelem[13] == 'SET_RED') {
                    jQuery("#sandgrid").setCell(rowid, 'insp_due_dt', '', { color: 'red' })
                }
                if (rowelem[14] == 'SET_RED') {
                    jQuery("#sandgrid").setCell(rowid, 'service_due_num', '', { color: 'red' })
                }
                if (rowelem[15] == 'SET_RED') {
                    jQuery("#sandgrid").setCell(rowid, 'tag_expire_dt', '', { color: 'red' })
                }
                if (rowelem[16] == 'SET_GREEN') {
                    jQuery("#sandgrid").setCell(rowid, 'equip_id', '', { color: 'green' })
                }
                if (rowelem[16] == 'SET_PURPLE') {
                    jQuery("#sandgrid").setCell(rowid, 'equip_id', '', { color: 'purple' })
                }
            },
            viewrecords: true,
            pager: jQuery('#sandgridp'),
            caption: 'Inventory'
        }).navGrid('#sandgridp',
     {}, //options
     {reloadAfterSubmit: false }, // edit options
     {reloadAfterSubmit: false }, // add options
     {reloadAfterSubmit: false }, // del options
     {} // search options
     );

        $('#sandgridp_center').remove();
        $('#sandgridp_right').remove();
    });
</script>