That's just got to do with if the main index for your forum is categories.php or ubbthreads.php you have to have at least one category - forums can only exist inside of a category, so without a category, you've got an expensive empty site. <img src="https://www.ubbcentral.com/boards/images/graemlins/wink.gif" alt="" />
This site here uses just one category.
categories.php - example:
https://www.ubbcentral.com/boards/categories.phpRequires the user to click the category before they see the forums.
ubbthreads.php - example:
https://www.ubbcentral.com/boards/ubbthreads.phpAllows the users to click on the forum right away.
The users control which page they see as the Main Index in their display prefs.
