Where you added:"DIR_WS_FUNCTIONS" to read: require(DIR_WS_FUNCTIONS . 'featured_faqs.php');
zen_start_featured_faqs();
zen_expire_featured_faqs();

Then you changed to this in version 2.1 to read:
require(DIR_WS_CLASSES . 'faq_category_tree.php');

require(DIR_WS_CLASSES . 'featued_faqs.php');
zen_start_featured_faqs();
Add a r to "featued_faqs.php to read "featured_faqs.php"
zen_expire_featured_faqs();
This should get you back up and running .. This file is located at includes/init_includes/init_faq.php