Спасибо за замечание. В результате выяснилось, что полная очистка таблицы assets приводит к тому, что невозможно зайти в панель управления. Очистив таблицу залил туда данные из дистрибутива Joomla 2.5.6. Не берусь сказать насколько это корректно но на текущий момент все работает.
INSERT INTO `префикс_assets` (`id`, `parent_id`, `lft`, `rgt`, `level`, `name`, `title`, `rules`)
VALUES
(1, 0, 1, 67, 0, 'root.1', 'Root Asset', '{"core.login.site":{"6":1,"2":1},"core.login.admin":{"6":1},"core.login.offline":{"6":1},"core.admin":{"8":1},"core.manage":{"7":1},"core.create":{"6":1,"3":1},"core.delete":{"6":1},"core.edit":{"6":1,"4":1},"core.edit.state":{"6":1,"5":1},"core.edit.own":{"6":1,"3":1}}'),
(2,1,1,2,1,'com_admin','com_admin','{}'),
(3,1,3,6,1,'com_banners','com_banners','{"core.admin":{"7":1},"core.manage":{"6":1},"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(4,1,7,8,1,'com_cache','com_cache','{"core.admin":{"7":1},"core.manage":{"7":1}}'),
(5,1,9,10,1,'com_checkin','com_checkin','{"core.admin":{"7":1},"core.manage":{"7":1}}'),
(6,1,11,12,1,'com_config','com_config','{}'),
(7,1,13,16,1,'com_contact','com_contact','{"core.admin":{"7":1},"core.manage":{"6":1},"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[],"core.edit.own":[]}'),
(8,1,17,20,1,'com_content','com_content','{"core.admin":{"7":1},"core.manage":{"6":1},"core.create":{"3":1},"core.delete":[],"core.edit":{"4":1},"core.edit.state":{"5":1},"core.edit.own":[]}'),
(9,1,21,22,1,'com_cpanel','com_cpanel','{}'),
(10,1,23,24,1,'com_installer','com_installer','{"core.admin":[],"core.manage":{"7":0},"core.delete":{"7":0},"core.edit.state":{"7":0}}'),
(11,1,25,26,1,'com_languages','com_languages','{"core.admin":{"7":1},"core.manage":[],"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(12,1,27,28,1,'com_login','com_login','{}'),
(13,1,29,30,1,'com_mailto','com_mailto','{}'),
(14,1,31,32,1,'com_massmail','com_massmail','{}'),
(15,1,33,34,1,'com_media','com_media','{"core.admin":{"7":1},"core.manage":{"6":1},"core.create":{"3":1},"core.delete":{"5":1}}'),
(16,1,35,36,1,'com_menus','com_menus','{"core.admin":{"7":1},"core.manage":[],"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(17,1,37,38,1,'com_messages','com_messages','{"core.admin":{"7":1},"core.manage":{"7":1}}'),
(18,1,39,40,1,'com_modules','com_modules','{"core.admin":{"7":1},"core.manage":[],"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(19,1,41,44,1,'com_newsfeeds','com_newsfeeds','{"core.admin":{"7":1},"core.manage":{"6":1},"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[],"core.edit.own":[]}'),
(20,1,45,46,1,'com_plugins','com_plugins','{"core.admin":{"7":1},"core.manage":[],"core.edit":[],"core.edit.state":[]}'),
(21,1,47,48,1,'com_redirect','com_redirect','{"core.admin":{"7":1},"core.manage":[]}'),
(22,1,49,50,1,'com_search','com_search','{"core.admin":{"7":1},"core.manage":{"6":1}}'),
(23,1,51,52,1,'com_templates','com_templates','{"core.admin":{"7":1},"core.manage":[],"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(24,1,53,56,1,'com_users','com_users','{"core.admin":{"7":1},"core.manage":[],"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(25,1,57,60,1,'com_weblinks','com_weblinks','{"core.admin":{"7":1},"core.manage":{"6":1},"core.create":{"3":1},"core.delete":[],"core.edit":{"4":1},"core.edit.state":{"5":1},"core.edit.own":[]}'),
(26,1,61,62,1,'com_wrapper','com_wrapper','{}'),
(27,8,18,19,2,'com_content.category.2','Uncategorised','{"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[],"core.edit.own":[]}'),
(28,3,4,5,2,'com_banners.category.3','Uncategorised','{"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(29,7,14,15,2,'com_contact.category.4','Uncategorised','{"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[],"core.edit.own":[]}'),
(30,19,42,43,2,'com_newsfeeds.category.5','Uncategorised','{"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[],"core.edit.own":[]}'),
(31,25,58,59,2,'com_weblinks.category.6','Uncategorised','{"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[],"core.edit.own":[]}'),
(32,24,54,55,1,'com_users.notes.category.7','Uncategorised','{"core.create":[],"core.delete":[],"core.edit":[],"core.edit.state":[]}'),
(33,1,63,64,1,'com_finder','com_finder','{"core.admin":{"7":1},"core.manage":{"6":1}}'),
(34,1,65,66,1,'com_joomlaupdate','com_joomlaupdate','{"core.admin":[],"core.manage":[],"core.delete":[],"core.edit.state":[]}');
# --------------------------------------