Session is cleared when Gridview Update Button is clicked

Question

I have a page (Order.aspx) which displays an order which has a specific FileNo, below I call this page from my (Default.aspx):

    LinkButton clickedButton = (LinkButton)sender;
    Session["FileNo"] = clickedButton.Text;
    Response.Redirect("~/Order.aspx");

In this order page there is a gridview control with the following sqldatasource, the below Datasource was successfully working and updating the database, but suddenly it started to update the database with null FileNo. I don't understand when does my Session["FileNo"] gets cleared. I can provide any extra code requested.

<asp:SqlDataSource ID="sds_OrderDetail" OnSelected="sds_OrderDetail_Selected" runat="server"
    ConnectionString="<%$ ConnectionStrings:MyDbConn %>" DeleteCommand="DELETE FROM [OrderDetail] WHERE [RowNo] = @RowNo"
    InsertCommand="INSERT INTO [OrderDetail] ([FileNo], [PONumber], [MaterialCode], [MaterialDescription], [MaterialCategory], [UnitOfMeasure], [Quantity], [ContainerType], [LoadingDate]) VALUES (@FileNo, @PONumber, @MaterialCode, @MaterialDescription, @MaterialCategory, @UnitOfMeasure, @Quantity, @ContainerType, @LoadingDate)"
    SelectCommand="SELECT * FROM [OrderDetail] WHERE ([FileNo] = @FileNo)" UpdateCommand="UPDATE [OrderDetail] SET [FileNo] = @FileNo, [PONumber] = @PONumber, [MaterialCode] = @MaterialCode, [MaterialDescription] = @MaterialDescription, [MaterialCategory] = @MaterialCategory, [UnitOfMeasure] = @UnitOfMeasure, [Quantity] = @Quantity, [ContainerType] = @ContainerType, [LoadingDate] = @LoadingDate WHERE [RowNo] = @RowNo">
    <SelectParameters>
        <asp:SessionParameter DefaultValue="-1" Name="FileNo" SessionField="FileNo" Type="Int32" />
    </SelectParameters>
    <DeleteParameters>
        <asp:Parameter Name="RowNo" Type="Int32" />
    </DeleteParameters>
    <InsertParameters>
        <asp:Parameter Name="FileNo" Type="Int32" />
        <asp:Parameter Name="PONumber" Type="String" />
        <asp:Parameter Name="MaterialCode" Type="String" />
        <asp:Parameter Name="MaterialDescription" Type="String" />
        <asp:Parameter Name="MaterialCategory" Type="String" />
        <asp:Parameter Name="UnitOfMeasure" Type="String" />
        <asp:Parameter Name="Quantity" Type="Int32" />
        <asp:Parameter Name="ContainerType" Type="String" />
        <asp:Parameter Name="LoadingDate" Type="String" />
    </InsertParameters>
    <UpdateParameters>
        <asp:Parameter Name="FileNo" Type="Int32" />
        <asp:Parameter Name="PONumber" Type="String" />
        <asp:Parameter Name="MaterialCode" Type="String" />
        <asp:Parameter Name="MaterialDescription" Type="String" />
        <asp:Parameter Name="MaterialCategory" Type="String" />
        <asp:Parameter Name="UnitOfMeasure" Type="String" />
        <asp:Parameter Name="Quantity" Type="Int32" />
        <asp:Parameter Name="ContainerType" Type="String" />
        <asp:Parameter Name="LoadingDate" Type="String" />
        <asp:Parameter Name="RowNo" Type="Int32" />
    </UpdateParameters>
</asp:SqlDataSource>

Answer 1

Other than select parameters, all the other parameters should include FileNo as SessionParameter, Session["FileNo"] is not cleared, it was not used.