Thanks Yudi, Handy and Ooi for the help.

I have changed

  var footerAmount1 = ISGetObject("WebGrid1").Tables["tableName"].GetFooterCellByName(htmlTable.rows.length - 1, "sel");
		     

to 

  var footerAmount1 = ISGetObject("WebGrid1").GetRootTable().GetElement(WG40.COLFOOTER, WG40.HTMLTABLE).cells[4];

and it works.

Regards

xin8

thank you very much Glenn!

i added your code in client side. It didn't work.

 But then i do it in server side. It is a success!

Here's the snippet to share:

 Private Sub WebGrid1_PrepareDataBinding(ByVal sender As Object, ByVal e As ISNet.WebUI.WebGrid.DataSourceEventArgs) Handles WebGrid1.PrepareDataBinding
        If Page.IsPostBack = False Then
            WebGrid1.RetrieveStructure()
        End If

        With WebGrid1.RootTable.Columns
            .GetNamedItem("Tick").Width = Unit.Pixel("30")
            .GetNamedItem("Tick").ColumnType = ISNet.WebUI.WebGrid.ColumnType.Custom

        End With
    End Sub

Thank you again.

Regards

xin8