Dropdownlist ดึงจาก DataBind() แล้วพอเลือกแล้ว SelectIndex ไม่ได้ครับ

            DT = New DataTable
            DT.Load(MyReader)
            DDLJob3.DataSource = DT
            DDLJob3.DataTextField = "JobName"
            DDLJob3.DataValueField = "JobName"
            DDLJob3.DataBind()
            MyReader.Close()

Protected Sub DDLJob1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DDLJob1.SelectedIndexChanged
        If DDLJob1.SelectedIndex = DDLJob1.Items.IndexOf(DDLJob1.Items.FindByValue("งานอื่นๆ")) Then
            txtJob1.Visible = True
        Else
            txtJob1.Visible = False
        End If
    End Sub