Sorting in jqGrid?

Question

Hello All, I am binding the jqgrid but the sorting is not working plaese can anyone tell why it is not working.I am posting the code here

jQuery(document).ready(function() { var TheGrid; var resp; jQuery("#registerUsers").jqGrid( { url: 'EventsList.aspx', datatype: "json", id: "Register_Id",

            colNames: ["", "Name", "Company Name", "Responsible Name", "Date/Time"],
            colModel: [
                      { name: 'RegId', index: 'RegId', width: 100, align: 'center', sortable: false , formatter: checkboxFormatter },
                      { name: 'GuestName', index: 'GuestName', width: 150, align: 'center', sorttype:'text', editoptions: { readonly: true, size: 10} },
                      { name: 'CompName', index: 'CompName', width: 150, align: 'center', sortable: true, editoptions: { readonly: true, size: 10} },
                      { name: 'RespName', index: 'RespName', width: 150, align: 'center', sortable: true,  editoptions: { readonly: true, size: 10} },
                      { name: 'DateTime', index: 'DateTime', width: 150, align: 'center', sortable: true,  editoptions: { readonly: true, size: 10} },

                     ],                
            rowNum: 10,
            rowList: [10, 20, 30],
            pager: jQuery('#Userpager'),
            sortname: 'RegId',
            sortorder: "asc",
            viewrecords: true,
            imgpath: '/scripts/themes/steel/images',
            caption: "Registered Users"

        });

    });

Please help me.

Thanks Ritz