MOSS: This page is not using a valid page layout.

Problem:
When creating a custom Site Definition containing Publishing features, the site creation succeeds, but when entering the site you receive error: "This page is not using a valid page layout. To correct the problem, edit page settings and select a valid page layout.""

Solution:
See that you have Type set in the File element under Modules -> Module in the ONET.XML of the Site Definition.

<File Url="default.aspx" NavBarHome="True" Type="GhostableInLibrary" Level="Draft">