Hi Daniel, my test site gave me theses errors on Joomla 2.5.7 :
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP Notice: Trying to get property of non-object in /var/www/aldra/libraries/joomla/updater/adapters/extension.php on line 193, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP Stack trace:, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 1. {main}() /var/www/aldra/administrator/index.php:0, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 2. JAdministrator->render() /var/www/aldra/administrator/index.php:52, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 3. JApplication->triggerEvent() /var/www/aldra/administrator/includes/application.php:204, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 4. JDispatcher->trigger() /var/www/aldra/libraries/joomla/application/application.php:642, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 5. JEvent->update() /var/www/aldra/libraries/joomla/event/dispatcher.php:161, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 6. call_user_func_array() /var/www/aldra/libraries/joomla/event/event.php:71, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 7. plgSystemCupdater->onAfterRender() /var/www/aldra/libraries/joomla/event/event.php:0, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 8. plgSystemCupdater->checkForUpdates() /var/www/aldra/plugins/system/cupdater/cupdater.php:48, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 9. JUpdater->findUpdates() /var/www/aldra/plugins/system/cupdater/cupdater.php:177, referer: http://localhost/
[Sun Sep 16 09:59:47 2012] [error] [client 127.0.0.1] PHP 10. JUpdaterExtension->findUpdate() /var/www/aldra/libraries/joomla/updater/updater.php:118, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP Notice: Trying to get property of non-object in /var/www/aldra/libraries/joomla/updater/adapters/collection.php on line 131, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP Stack trace:, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 1. {main}() /var/www/aldra/administrator/index.php:0, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 2. JAdministrator->render() /var/www/aldra/administrator/index.php:52, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 3. JApplication->triggerEvent() /var/www/aldra/administrator/includes/application.php:204, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 4. JDispatcher->trigger() /var/www/aldra/libraries/joomla/application/application.php:642, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 5. JEvent->update() /var/www/aldra/libraries/joomla/event/dispatcher.php:161, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 6. call_user_func_array() /var/www/aldra/libraries/joomla/event/event.php:71, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 7. plgSystemCupdater->onAfterRender() /var/www/aldra/libraries/joomla/event/event.php:0, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 8. plgSystemCupdater->checkForUpdates() /var/www/aldra/plugins/system/cupdater/cupdater.php:48, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 9. JUpdater->findUpdates() /var/www/aldra/plugins/system/cupdater/cupdater.php:177, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 10. JUpdaterCollection->findUpdate() /var/www/aldra/libraries/joomla/updater/updater.php:118, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 11. xml_parse() /var/www/aldra/libraries/joomla/updater/adapters/collection.php:243, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 12. JUpdaterCollection->_startElement() /var/www/aldra/libraries/joomla/updater/adapters/collection.php:0, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP Notice: Trying to get property of non-object in /var/www/aldra/libraries/joomla/updater/adapters/collection.php on line 131, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP Stack trace:, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 1. {main}() /var/www/aldra/administrator/index.php:0, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 2. JAdministrator->render() /var/www/aldra/administrator/index.php:52, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 3. JApplication->triggerEvent() /var/www/aldra/administrator/includes/application.php:204, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 4. JDispatcher->trigger() /var/www/aldra/libraries/joomla/application/application.php:642, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 5. JEvent->update() /var/www/aldra/libraries/joomla/event/dispatcher.php:161, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 6. call_user_func_array() /var/www/aldra/libraries/joomla/event/event.php:71, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 7. plgSystemCupdater->onAfterRender() /var/www/aldra/libraries/joomla/event/event.php:0, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 8. plgSystemCupdater->checkForUpdates() /var/www/aldra/plugins/system/cupdater/cupdater.php:48, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 9. JUpdater->findUpdates() /var/www/aldra/plugins/system/cupdater/cupdater.php:177, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 10. JUpdaterCollection->findUpdate() /var/www/aldra/libraries/joomla/updater/updater.php:118, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 11. xml_parse() /var/www/aldra/libraries/joomla/updater/adapters/collection.php:243, referer: http://localhost/
[Sun Sep 16 09:59:48 2012] [error] [client 127.0.0.1] PHP 12. JUpdaterCollection->_startElement() /var/www/aldra/libraries/joomla/updater/adapters/collection.php:0, referer: http://localhost/