SqlDataSource Refresh Problem

Dear sirs:

I have a Web Form with an SqlDataSource with a simple select statement, and a GridView control that is tied to it. There is a ComboBox (which provides the filter-command parameter) and a Submit button as well. When a selection is made (the first time) in the combo box and then the submit button is clicked, the Selecting Event for the SqlDataSource fires and the code works perfect.

However, on subsequent "submits" with the button and selecting a different month from the combo box, I cannot get that event to fire again. What do I need to do to get this event to fire everytime the submit button is clicked and a new selection made from the drop down combo box; thus letting me know that new data is being fetched from the database?

Here is the code for the SqlDataSource:

<<asp:SqlDataSource
ID = "sqlDataSourceG5WingRailCar"
runat = "server"
ConnectionString = "<%$ ConnectionStrings:oracleConnectionString %>"
ProviderName = "<%$ ConnectionStrings:oracleConnectionString.ProviderName %>"
SelectCommand = "select distinct to_date( mh.historydatetime , 'DD-MM-YYYY' ) ,
                            rh.movedescription ,
                            ( mds.pct_util * count( rh.movedescription ) )

                            from requesthistory rh

                            inner join movehistory mh on rh.itd_number = mh.itd_number
                            inner join movedescription mds on rh.movedescr_id = mds.movedescr_id

                            where rh.movedescr_id = 1 AND mh.discrepancy_id = 25 AND EXTRACT(MONTH FROM mh.historydatetime) = :MONTH_ID

                            group by to_date( mh.historydatetime , 'DD-MM-YYYY' ) ,
                                         rh.movedescription ,
                                         mds.pct_util

                            order by to_date( mh.historydatetime , 'DD-MM-YYYY' )"

önSelecting="sqlDataSourceG5WingRailCar_Selecting" >
<<SelectParameters>>

<<asp:ControlParameter
ControlID = "dropDownListMonth"
Name = "MONTH_ID"
PropertyName = "SelectedValue" >>

<</asp:ControlParameter>>

<</SelectParameters>>

<</asp:SqlDataSource>>

There really is no code for the Selecting Event, other than just capturing some text into a label when the event occurs (for testing purposes).

Thanks