After you loaded your control definition from the ascx and retrieved the embedded controls using FindControl(), you notice that the child controls’ events do not fire anymore.
While the Page_Load and other Page_ events fire correctly for the control that loaded the ascx, the events for the controls inside the ascx are ignored: You need to wire them explicitly in code.
If, for example, your ascx contains a button declaration
<asp:Button ID="btnCalc" runat="server" OnClick="btnCalc_Click" />
you need to retrieve the control and wire the event like this
btnCalc = (Button)this.FindControl("btnCalc"); btnCalc.Click += btnCalc_Click;