There is no check during deployment if the URL you provided in the descriptor actually points to a valid JSP/Servlet. Check that the jsp is actually available via a request dispatcher under the provided URL...
there should also be information in the log about how far the invocation gets (i.e. if it finds the layout or not)
I still can't see any errors or what I might be doing wrong. Is there an example deployment war file for a layout?
I have a custom layout and it is fine. Using 2.4GA.
you can contact me by e-mail so I send you the war of my layouts.
e-mail adress via my web site.
I suggest to start from one of the provided layout, put it in your war exactly as it is provided, then check it works.
then change thing one step by one step, and check each time it works.
I've gotten to work in both 2.4.1 and 2.6.
Turns out you can't hot-deploy a custom layout. Despite being recognized by the portal and allowing you to set it in the admin tool, it renders a blank page until you restart the server, at which point the layout works correctly.
I wasted a day nearly tearing my hair out before I discovered this.