Combobox in datagrid is not working(Not droping down ):Just showing topmost value

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C#3.0

C#

// in the gdvReturnOrder_CellMouseUp(

if (e.ColumnIndex == 0 && e.RowIndex != -1)
            //{
                DataGridViewComboBoxCell comboCell =
                   gdvReturnOrder.Rows[e.RowIndex].Cells["Column9"] as DataGridViewComboBoxCell;

                if (comboCell != null)
                {
                    comboCell.Value = comboCell.Selected;
                }

And loaded the the column through..this way:(On Button Click)
//gdvReturnOrder_Load();
<pre><pre lang="text">for (int index = 0; index < this.gdvReturnOrder.Rows.Count; index++)
                {
                        DataGridViewComboBoxCell dc = new DataGridViewComboBoxCell();
                        dc.Items.Add("Good");
                        dc.Items.Add("Loss");
                        dc.Items.Add("Damaged");
                        this.gdvReturnOrder.Rows[index].Cells["Column9"] = dc;
                        this.gdvReturnOrder.Rows[index].Cells["Column9"].Value = dc.Items[0];
                 }

It is showing values(Top most value:Good) bt I am not able to select it Is some Setting of Combobox coloumn has to be set to make it work?