All what I got when I tried to register ...

DEBUG MODE

SQL Error : 1054 Unknown column 'g.group_id' in 'on clause'

SELECT ug.user_id, g.group_id as g_id, g.group_name , u.user_posts, g.group_count FROM sonofshun_phpbb_groups g, sonofshun_phpbb_users u LEFT JOIN sonofshun_phpbb_user_group ug ON g.group_id=ug.group_id AND ug.user_id=27648 WHERE u.user_id=27648 AND ug.user_id is NULL AND g.group_count=0 AND g.group_single_user=0 AND g.group_moderator<>27648

Line : 731
File : usercp_register.php