cast is invalid when attempting to grab inserted ID

I am attempting to grab the recently inserted ID for a table, but I keep receiving a casting error. The item always contains NULL, and I am not sure why. I am following the instructions located here: http://www.mikesdotnetting.com/Article/54/Getting-the-identity-of-the-most-recently-added-record

Here is my SqlDataSource:

<asp:SqlDataSource ID="SqlDataSource2" runat="server" 
    ConnectionString="<%$ ConnectionStrings:NH_SWAGConnectionString %>"             
    InsertCommand="INSERT INTO [tblOrders] ([OrderDate], [OrderTotal], [OrderAccount], [OrderCostCentre]) VALUES (@OrderDate, @OrderTotal, @OrderAccount, @OrderCostCentre); SET @OrderNewID = SCOPE_IDENTITY()" 
    SelectCommand="SELECT * FROM [tblOrders]" 
    UpdateCommand="UPDATE [tblOrders] SET [OrderDate] = @OrderDate, [Order开发者_如何学运维Total] = @OrderTotal, [OrderAccount] = @OrderAccount, [OrderCostCentre] = @OrderCostCentre WHERE [OrderID] = @original_OrderID AND [OrderDate] = @original_OrderDate AND [OrderTotal] = @original_OrderTotal AND [OrderAccount] = @original_OrderAccount AND [OrderCostCentre] = @original_OrderCostCentre"            
    ConflictDetection="CompareAllValues" 
    OldValuesParameterFormatString="original_{0}"
    OnInserting="SqlDataSource2_Inserting"
    OnInserted="SqlDataSource2_Inserted">
    <InsertParameters>
        <asp:Parameter Direction="Output" Name="OrderNewId" Type="Int32" />
    </InsertParameters>
    <UpdateParameters>
        <asp:Parameter Name="OrderDate" Type="DateTime" />
        <asp:Parameter Name="OrderTotal" Type="Decimal" />
        <asp:Parameter Name="OrderAccount" Type="String" />
        <asp:Parameter Name="OrderCostCentre" Type="String" />
        <asp:Parameter Name="original_OrderID" Type="Int32" />
        <asp:Parameter Name="original_OrderDate" Type="DateTime" />
        <asp:Parameter Name="original_OrderTotal" Type="Decimal" />
        <asp:Parameter Name="original_OrderAccount" Type="String" />
        <asp:Parameter Name="original_OrderCostCentre" Type="String" />
    </UpdateParameters>
</asp:SqlDataSource>

Here is the code behind inserting the new record, and calling SCOPE_IDENTITY() to grab the new ID:

protected void btnOrder_Click(object sender, EventArgs e)
{
    //Add entry to Order Table    

    SqlDataSource2.InsertParameters.Add("OrderDate", DateTime.Now.ToString("MMMM dd, yyyy"));
    SqlDataSource2.InsertParameters.Add("OrderTotal", "0");
    SqlDataSource2.InsertParameters.Add("OrderAccount", ItmUser);
    SqlDataSource2.InsertParameters.Add("OrderCostCentre", ItmCostCode.Text);

    SqlDataSource2.Insert();
}

protected void SqlDataSource2_Inserted(object sender, SqlDataSourceStatusEventArgs e)
{
    OrderNewID = (int)e.Command.Parameters["@OrderNewId"].Value;
}

Why @OrderNewId above is NULL?

Ok I got it figured. Instead of using SET I used SELECT in the InsertQuery:

INSERT INTO [tblOrders] ([OrderDate], [OrderTotal], [OrderAccount], [OrderCostCentre]) VALUES (@OrderDate, @OrderTotal, @OrderAccount, @OrderCostCentre); SELECT @OrderNewID = SCOPE_IDENTITY()