Error cargando Componente: com_joomlaupdate, 1
Error cargando Componente: com_installer, 1

Al parecer “algo” ha borrado los registros com_installer & com_joomlaupdate de la tabla #__extensions. Tras obtener los registros de un Joomla 2.5.4 recién instalado y restaurarlos en la base de datos que daba error desaparecen los mensajes de error.

Para solucionar el error ejecuta esta query de SQL reemplazando #__extensions con el nombre de tu tabla de extensiones. Por ejemplo si el prefijo de tu base de datos jml25_ sustituye #__extensions con jml25_extensions

INSERT INTO `#__extensions` (`extension_id`, `name`, `type`, `element`, `folder`, `client_id`, `enabled`, `access`, `protected`, `manifest_cache`, `params`, `custom_data`, `system_data`, `checked_out`, `checked_out_time`, `ordering`, `state`) VALUES (10, 'com_installer', 'component', 'com_installer', '', 1, 1, 1, 1, '{"legacy":false,"name":"com_installer","type":"component","creationDate":"April 2006","author":"Joomla! Project","copyright":"(C) 2005 - 2012 Open Source Matters. All rights reserved.\\t","authorEmail":"admin@joomla.org","authorUrl":"www.joomla.org","version":"2.5.0","description":"COM_INSTALLER_XML_DESCRIPTION","group":""}', '{}', '', '', 0, '0000-00-00 00:00:00', 0, 0);

INSERT INTO `#__extensions` (`extension_id`, `name`, `type`, `element`, `folder`, `client_id`, `enabled`, `access`, `protected`, `manifest_cache`, `params`, `custom_data`, `system_data`, `checked_out`, `checked_out_time`, `ordering`, `state`) VALUES (28, 'com_joomlaupdate', 'component', 'com_joomlaupdate', '', 1, 1, 0, 1, '{"legacy":false,"name":"com_joomlaupdate","type":"component","creationDate":"February 2012","author":"Joomla! Project","copyright":"(C) 2005 - 2012 Open Source Matters. All rights reserved.\\t","authorEmail":"admin@joomla.org","authorUrl":"www.joomla.org","version":"2.5.0","description":"COM_JOOMLAUPDATE_XML_DESCRIPTION","group":""}', '{}', '', '', 0, '0000-00-00 00:00:00', 0, 0);

Espero que a alguien le ahorre algo de tiempo.

Error loading Component: com_joomlaupdate, 1
Error loading Component: com_installer, 1

Seems that “something” deleted com_installer & com_joomlaupdate entries in the #__extensions table. I got the deleted values from a clean Joomla 2.5.4. install and after restoring them to the broken database all works fine again.

So to solve the problem you just have to run a sql query replacing #__extensions with your exact table name so if your database prefix is, for example, jml25_ replace #__extensions with jml25_extensions

INSERT INTO `#__extensions` (`extension_id`, `name`, `type`, `element`, `folder`, `client_id`, `enabled`, `access`, `protected`, `manifest_cache`, `params`, `custom_data`, `system_data`, `checked_out`, `checked_out_time`, `ordering`, `state`) VALUES (10, 'com_installer', 'component', 'com_installer', '', 1, 1, 1, 1, '{"legacy":false,"name":"com_installer","type":"component","creationDate":"April 2006","author":"Joomla! Project","copyright":"(C) 2005 - 2012 Open Source Matters. All rights reserved.\\t","authorEmail":"admin@joomla.org","authorUrl":"www.joomla.org","version":"2.5.0","description":"COM_INSTALLER_XML_DESCRIPTION","group":""}', '{}', '', '', 0, '0000-00-00 00:00:00', 0, 0);

INSERT INTO `#__extensions` (`extension_id`, `name`, `type`, `element`, `folder`, `client_id`, `enabled`, `access`, `protected`, `manifest_cache`, `params`, `custom_data`, `system_data`, `checked_out`, `checked_out_time`, `ordering`, `state`) VALUES (28, 'com_joomlaupdate', 'component', 'com_joomlaupdate', '', 1, 1, 0, 1, '{"legacy":false,"name":"com_joomlaupdate","type":"component","creationDate":"February 2012","author":"Joomla! Project","copyright":"(C) 2005 - 2012 Open Source Matters. All rights reserved.\\t","authorEmail":"admin@joomla.org","authorUrl":"www.joomla.org","version":"2.5.0","description":"COM_JOOMLAUPDATE_XML_DESCRIPTION","group":""}', '{}', '', '', 0, '0000-00-00 00:00:00', 0, 0);

Hope this helps.