asp.net - Cannot acess a class from virtual directory

Question

Using C# in an ASP.NET application, I have a class Class1 in the App_Code folder. I can create a c1 object and use it in Default.aspx.cs page, and it works fine. However, when I create a Virtual Directory and run it from there, it gives me the following error:

CS0246: The type or namespace name 'Class1' could not be found (are you missing a using directive