The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>)

I was recently adding Script Bundling to my ASP.NET Web Forms Web Application, when I suddenly encountered this error message:

The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>)

Well, this was how my code was placed on the page originally:

<%: Scripts.Render("~/bundles/jquery") %>
<%: Scripts.Render("~/bundles/jqueryUI") %>

However, after taking a look at Microsoft's solution to this problem, I discovered that I had to surround these code blocks with a PlaceHolder control!!

Therefore, I had to modify my code to look like the following:

<asp:PlaceHolder runat="server">
        <%: Scripts.Render("~/bundles/jquery") %>
        <%: Scripts.Render("~/bundles/jqueryUI") %>
        <%: Scripts.Render("~/scripts/custom") %>
</asp:PlaceHolder>

Once I did that, my code worked just as expected!!