Forum's Order By drop down list is empty?

If you notice that the Order By drop down list in your forums thread listing is empty, please go to the admin CP -> forum management interface for each individual forum that has this problem, and check the box beside the order by method you want to allow.

This setting is provided for you to limit the sorting criteria on certain forums (for whatever reasons), and to preserve performance as well by allowing you to eliminate character based sorting (member name; subject) on busy forums.