Going through Joe Stangler's Custom Principal Tutorial and getting a cast error...

Using VS2010 .Net 4.0.
I'm going through Joe Stangler's Custom Principal Tutorial video and I keep getting the following error
Unable to cast object of type 'System.Web.Security.FormsIdentity' to type 'ASPSecurityTutorial.CustomIdentity'.
one this line...
CustomIdentity ident = (CustomIdentity)User.Identity;
in the Default.aspx page after the request is authenticated.
I'm also having problems putting the class code in the App_Code folder or any module in any subfolder within the project. Other pages just don't see them. I'm creating the d ...