Email format is correct while adding the record but incorrect format error while editing the same record JQgrid

jQuery("#jQGridDemo").jqGrid({
               url: 'http://localhost:63453/JQGridHandler.ashx',
               datatype: "json",
               colNames: ['Id', 'First Name','Address','Email'],
               colModel: [
               { name: 'id', index: 'id', width: 20, stype: 'text', editable: true, editrules: { size: 20 } },
               { name: 'name', index: 'name', width: 150, editable: true },
               { name: 'address', index: 'address', width: 150, editable: true },
               { name: 'email', index: 'email', width: 150, editable: true, editrules: {required:true, email:true} },
               ],
               rowNum: 50,
               sortname: 'id',
               viewrecords: true,
               sortorder: "desc",
               caption: "List Employee Details",
               autowidth: true,
               pager: '#jQGridDemoPager',
               editurl: 'http://localhost:63453/JQGridHandler.ashx'
           });

           $('#jQGridDemo').jqGrid('navGrid', '#jQGridDemoPager',
                  {
                      edit: true,
                      add: true,
                      del: true,
                      search: true,
                      refresh: true,
                      searchtext: 'search',
                      addtext: 'Add',
                      edittext: 'edit',
                      deltext: 'delete'

if (strOperation == "add")
            {
                SqlConnection con = new SqlConnection("server=Ignitor-PC5;database=JQGridTest;uid=sa;pwd=Ignitor1234");
                int intId = Convert.ToInt32(forms.Get("id"));
                string strFirstName = forms.Get("name").ToString();
                string straddress = forms.Get("address").ToString();
                string stremail = forms.Get("email").ToString();
                con.Open();
                string QryString = "insert into grid  values(" + intId + " ,' " + strFirstName + " ',' " + straddress + "' ,' " + stremail + " ')";
              
               SqlCommand cmd = new SqlCommand(QryString, con);
               cmd.ExecuteNonQuery();
               strResponse = " Record added successfully";
               context.Response.Write(strResponse);
               con.Close();
            }
            else if (strOperation == "edit")
            {
                SqlConnection con = new SqlConnection("server=Ignitor-PC5;database=JQGridTest;uid=sa;pwd=Ignitor1234");
                int intId = Convert.ToInt32(forms.Get("id"));
                string strFirstName = forms.Get("name").ToString();
                string straddress = forms.Get("address").ToString();
                string stremail = forms.Get("email").ToString();
                
                con.Open();
                SqlCommand cmd = new SqlCommand("update grid set name=' " + 
                    strFirstName + "',address='" + straddress + "' ,email='" + stremail + " ' where id= " + intId + "  ", con);
                cmd.ExecuteNonQuery();
                strResponse = "Record edited successfully";
                context.Response.Write(strResponse);
                con.Close();
            }