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Editorial Team
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Asked: 2026-05-18T20:20:00+00:00

I am learning custom controls and just finished my first one. The problem is

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I am learning custom controls and just finished my first one. The problem is that I am struggling to register it in my web config and have the compiler recognize it. Right now this results in a YSOD about the reference to the control.

note: exact error – Error Unknown server tag ‘cc:LblTextBox’.

Thank you!

Web Config

//..
//..
     <pages>
       <controls>
         <add tagPrefix="cc" namespace="Controls.Server"/>
       </controls>
     </pages>
</system.web>

The control code-behind

namespace Controls.Server
{
    public class LblTextBox : CompositeControl
    {
       //...
    }
}

mark-up

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="ControlsMain.aspx.cs" Inherits="Pages_ControlsMain" Trace="true" %>

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
 <head runat="server">
     <title>Controls Area</title>
 </head>
 <body>
    <form id="form1" runat="server">
    <div>
          First attempt at a simple composite control <br />
         <cc:LblTextBox ID="ccLblTbHybrid" runat="server" LabelText="Name:" />
   </div>
   </form>
 </body>

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1 Answer

  1. Editorial Team

    The issue stemmed from setting up the project as an ASP.Net Web Site

    This has a drawback because the name of your assembly is not known till runtime.

    I recreated the project as a ASP.Net Web Application, allowing for procompilation of the DLLs …. thus giving me the ability to give the project a namespace.

    I then added abe’s suggestion into the entry and all is working now

    <add tagPrefix="cc" namespace="Controls.Server" assembly="DevLore"/>
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