That is not what I told you to do! <if test="showSubForums:|:$forum_data['show_subforums'] AND count( $forum_data['subforums'] ) AND $forum_data['show_subforums'] AND $_data['cat_data']['id']!=18">
Should have stated that in the beginning.
Since all skins are not the same this line may be different. find
<if test="showSubForums:|:$forum_data['show_subforums'] AND count( $forum_data['subforums'] ) AND $forum_data['show_subforums']">
change to
<if test="showSubForums:|:$forum_data['show_subforums'] AND count( $forum_data['subforums'] ) AND $forum_data['show_subforums'] AND $_data['cat_data']['id']!=??">
Change the ?? to the category number