Next step that I took, is to replace here:

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="ManageAttributes.ascx.cs"
    Inherits="CodexStar.Modules.VideoLinker.ManageAttributes" %>

CodeBehind by CodeFile

And, I also deleted the designer files. Now I have another problem. The controller class is not found.

Error    29    The type or namespace name 'VideoLinkerController' could not be found (are you missing a using directive or an assembly reference?)    C:\Server\TestSite\DotNetNuke\Website\DesktopModules\VideoLinker\VideoDetail.ascx.cs    35   

Here are the headers:

ASCX file:

using System;
using System.Collections;
using System.Web.UI.WebControls;
// DNN
using DotNetNuke;
using DotNetNuke.Common;
using DotNetNuke.Common.Utilities;
using DotNetNuke.Entities.Modules;
using DotNetNuke.Services.Exceptions;
using DotNetNuke.Services.Localization;


namespace CodexStar.Modules.VideoLinker
{

    /// -----------------------------------------------------------------------------
    /// <summary>
    /// The EditVideoLinker class is used to manage content
    /// </summary>
    /// <remarks>
    /// </remarks>
    /// <history>
    /// </history>
    /// -----------------------------------------------------------------------------
    partial class EditVideoLinker : PortalModuleBase
    {...}

}

CONTROLLER CLASS:

using System;
using System.Configuration;
using System.Data;
using System.Xml;
using System.Web;
using System.Collections.Generic;

using DotNetNuke;
using DotNetNuke.Common;
using DotNetNuke.Common.Utilities;
using DotNetNuke.Services.Search;
using DotNetNuke.Entities.Modules;

namespace CodexStar.Modules.VideoLinker
{

    /// -----------------------------------------------------------------------------
    /// <summary>
    /// The Controller class for VideoLinker
    /// </summary>
    /// <remarks>
    /// </remarks>
    /// <history>
    /// </history>
    /// -----------------------------------------------------------------------------
    public class VideoLinkerController
    {...}

}

Reference problems... Maybe I have done something wrong in the module creation procedure. Correct me please.