You cannot use <%= with a server control. You should use <%# and databind:
Backend
[Bindable(true)] public Range Range { get; set; }
Frontend
<uc:PopularItems ID="myControl" Range="<%# Range %>" runat="server" />
Backend page
if(! IsPostBack) { myControl.DataBind(); // or, to bind each control in the page: // this.DataBind(); }
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