Cannot bind to the new value member. in c#

hello every one, well my problem is that i m binding my data in combo box but its not working just check it now what is the problem in there sending you code.... code//////////////// private void show_description_details() { try { cb_contract_description.Items.Add("Select Description"); DataSet ds1 = new DataSet(); ds1 = gBL.show_description_list(); DataRow r = ds1.Tables[0].NewRow(); r["Description"] = "Select Description"; cb_contract_description.DataSource = ds1.Tables[0]; cb_contract_description.DisplayMember = "Description"; cb_contract_description.ValueMember = "Parent_Contract_ID"; cb_section_list.DataBindings.Clear(); cb_section_list.DataBindings.Add("text", ds1.Tables[0],"Under_Section"); } catch (Exception ex) { MessageBox.Show(ex.Message); } } plz reply me as soon as possible thanks in advance