ChatBox Coding in ASP.net error in globle.asax ,darective reference is not found

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ASP.NET

sir
i try to make a chat box in asp.net but i have there is a error in globle .asax page.asseble is not found i am sending u code of golobe.asax page please help me

<%@ Application Language="C#" %>
<%@ Import Namespace="ASPNETChat" %>
<%@ Import Namespace="System.Threading " %>
<script  runat="server">
    void Application_Start(object sender, EventArgs e) 
    {
        System.Threading.Timer ChatRoomsCleanerTimer = new System.Threading.Timer(new TimerCallback(ChatEngine.CleanChatRooms), null, 1200000, 1200000);
    }
    
    void Application_End(object sender, EventArgs e) 
    {
        //  Code that runs on application shutdown
    }
        
    void Application_Error(object sender, EventArgs e) 
    { 
        // Code that runs when an unhandled error occurs
    }
    void Session_Start(object sender, EventArgs e) 
    {
        // Code that runs when a new session is started
    }
    void Session_End(object sender, EventArgs e) 
    {
        // Code that runs when a session ends. 
        // Note: The Session_End event is raised only when the sessionstate mode
        // is set to InProc in the Web.config file. If session mode is set to StateServer 
        // or SQLServer, the event is not raised.
    }       
</script>