If you have used a Page that effectively uses a codebehind classname
that is the same as say the Login control, that is Login, e.g. your
page was called Login.aspx, then when you pre-compile (publish) the web
site as an updateable web site, the aspx is retained and tries to
compile against a type called Login in the code behind. It does not
resolve to be that in the codebehind assembly

Try using a classname for your codebehind and defined in the inherits
that does not clash with a type in System.Web, e.g. LoginPage, or
qualify the class and therefore the inherits statement with a
namespace, e.g.
in the .aspx file:

<%@ page … inherits=”MyNameSpace.Login” %.
in the code behind file:

namespace MyNameSpace

{ public partial class Login : System.Web.UI.Page

{

..

}

}