Problem with Combobox in Datagridview

                if (ds.Tables.Count > 0)
                {
                    if (ds.Tables["ClsIndex"].Rows.Count > 0)
                    {
                        dataGrdBenClassIndex.Columns.Clear();
                        dataGrdBenClassIndex.AutoGenerateColumns = false;
                        dataGrdBenClassIndex.DataSource = ds.Tables[0];

                        DataGridViewTextBoxColumn classColumn = new DataGridViewTextBoxColumn();
                        classColumn.HeaderText = "Class";
                        classColumn.Name = "CLASS";
                        classColumn.Width = 150;
                        classColumn.DataPropertyName = "Class";
                        classColumn.CellTemplate = new DataGridViewTextBoxCell();
                        classColumn.ReadOnly = false;
                        classColumn.ToolTipText = "Double Click this cell to change the class name";
                        classColumn.HeaderCell.Style.Alignment = DataGridViewContentAlignment.MiddleCenter;
                        dataGrdBenClassIndex.Columns.Add(classColumn);

                        DataGridViewComboBoxColumn typeColumn = new DataGridViewComboBoxColumn();
                        typeColumn.Name = "TYPE";                        
                        typeColumn.DataPropertyName = "Type";
                        typeColumn.DisplayMember = "Type";
                        typeColumn.DataSource = ds.Tables[0];
                        typeColumn.HeaderText = "Type";                        
                        typeColumn.ValueType = typeof(string);
                        typeColumn.DisplayStyle = DataGridViewComboBoxDisplayStyle.ComboBox;
                        typeColumn.Width = 220;
                        typeColumn.SortMode = DataGridViewColumnSortMode.NotSortable;
                        typeColumn.Sorted = false;
                        typeColumn.ReadOnly = false;
                        typeColumn.HeaderCell.Style.Alignment = DataGridViewContentAlignment.MiddleCenter;
                        typeColumn.ToolTipText = "Please select Type";                        
                        dataGrdBenClassIndex.Columns.Add(typeColumn);
}
}