CS0246: The type or namespace name 'Logic' could not be found (are you missing a using directive or an assembly reference?)

this is the error msg line:  Line 15: using Logic;
  here's is my source code.
home1.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
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