Asp.net dropdown tooltip Working only first time select

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ASP.NET

SQL-Server

This is my code this code only worikg for at a one time,my selection wrong i try to select another one tooltip not working.how to fix this eror .any one can help me.

//tooltip

      int ItemCount = dropdownConsignee.Items.Count;
                     for (int i = 0; i < ItemCount; i++)
                     {
dropdownConsignee.Items[i].Attributes.Add("Title", Ds.Tables[0].Rows[i]["Address"].ToString());
                     }
                     dropdownConsignee.Items.Insert(0, new ListItem("Select", "Address"));
                     dropdownConsignee.SelectedItem.Selected = false;
                     dropdownConsignee.Items.FindByText("Select").Selected = true;

Tnahk you