new Ext.grid.RowSelectionModel({singleSelect:true}) coolite gridpanel ?

[Hualin Yuan]

    RowSelectionModel rowSelectionModel = new RowSelectionModel();
            rowSelectionModel.SingleSelect = true;
                       MyGridPanel.SelectionModel.Add(rowSelectionModel);

Error:
Only one items available
Who can help me?</PRE>