Imported From: http://groups.google.com/group/in-portal-bugs/browse_thread/thread/80df2deaeb1f2c64#
If user visits url of a page, that doesn't exist yet, then it will be marked
as "Not Found" in CachedUrls table.
If administrator will create such page later, then it will be shown as "Not
Found" at Front-end.
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Best Regards,