Dla ułatwienia powiem, że stało się to po aktualizacji forum - już nie pamiętam czy między 3.1.1 a 3.1.2, ale gdzieś w tych okolicach. Cóż, trzeba przejść do edycji SQL i uzupełnić pole o nazwie app w tabeli o nazwie rc_classes. Pewnie masz to pole puste. Więc masz schemat i uzupełniaj:
INSERT INTO rc_classes (com_id, onoff, class_title, class_desc, author, author_url, pversion, my_class, group_can_report, mod_group_perm, extra_data, lockd, app) VALUES
(1, 1, 'Simple Plugin Example', 'Plugin that does not require any programming, but does need to be configured.', 'Invision Power Services, Inc', 'http://invisionpower.com', 'v1.0', 'default', ',3,4,6,', ',4,6,', 'a:5:{s:14:"required_input";a:1:{s:8:"video_id";s:13:"[^A-Za-z0-9_]";}s:10:"string_url";s:41:"http://www.youtube.com/watch?v={video_id}";s:12:"string_title";s:25:"#PAGE_TITLE# ({video_id})";s:13:"section_title";s:7:"YouTube";s:11:"section_url";s:22:"http://www.youtube.com";}', 1, 'core');
INSERT INTO rc_classes (com_id, onoff, class_title, class_desc, author, author_url, pversion, my_class, group_can_report, mod_group_perm, extra_data, lockd, app) VALUES
(2, 1, 'Forum Plugin', 'This is the plugin used for reporting posts on the forum.', 'Invision Power Services, Inc', 'http://invisionpower.com', 'v1.0', 'post', ',1,2,3,4,6,', ',4,6,', 'a:1:{s:15:"report_supermod";i:1;}', 0, 'forums');
INSERT INTO rc_classes (com_id, onoff, class_title, class_desc, author, author_url, pversion, my_class, group_can_report, mod_group_perm, extra_data, lockd, app) VALUES
(3, 1, 'Private Messages Plugin', 'This plugin allows private messages to be reported', 'Invision Power Services, Inc', 'http://invisionpower.com', 'v1.0', 'messages', ',1,2,3,4,6,', ',4,6,', 'a:1:{s:18:"plugi_messages_add";s:5:"4";}', 1, 'members');
INSERT INTO rc_classes (com_id, onoff, class_title, class_desc, author, author_url, pversion, my_class, group_can_report, mod_group_perm, extra_data, lockd, app) VALUES
(4, 1, 'Member Profiles', 'Allows you to report member profiles', 'Invision Power Services, Inc', 'http://invisionpower.com', 'v1.0', 'profiles', ',1,2,3,4,6,', ',4,6,', 'N;', 1, 'members');
INSERT INTO rc_classes (com_id, onoff, class_title, class_desc, author, author_url, pversion, my_class, group_can_report, mod_group_perm, extra_data, lockd, app) VALUES
(5, 1, 'Calendar Plugin', 'Allows calendar entries to be reported', 'Invision Power Services, Inc', 'http://invisionpower.com', 'v1.0', 'calendar', ',1,2,3,4,6,', ',4,6,', 'N;', 1, 'calendar');