I have the same problem and nothing of the previously mentioned advices helped.
My Joomla version 2.5.2 works fine. I installed a backup on a different site and this version was OK as well until I installed Joomla version 2.5.6. After logout no administrator login was possible: Without any error message the same login screen reappeared. Normal user access to the pages works fine.
I checked the session cookies with firebug on both versions and the content of the database table LBA_session. In 2.5.6 there was
no user information in the session table. I add a sql dump of both cases below.
I need urgent help since I can't upgrade any of my Joomla sites!
v252 sql dump:Code:
INSERT INTO `LBA_session` (`session_id`, `client_id`, `guest`, `time`, `data`, `userid`, `username`, `usertype`) VALUES
('d72b24325c344a0286fcb1dfc412b48b', 1, 0, '1342566080', '__default|a:8:{s:15:"session.counter";i:5;s:19:"session.timer.start";i:1342566072;s:18:"session.timer.last";i:1342566078;s:17:"session.timer.now";i:1342566080;s:22:"session.client.browser";s:74:"Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20100101 Firefox/13.0.1";s:8:"registry";O:9:"JRegistry":1:{s:7:"\0*\0data";O:8:"stdClass":2:{s:11:"application";O:8:"stdClass":1:{s:4:"lang";s:0:"";}s:13:"com_installer";O:8:"stdClass":2:{s:7:"message";s:0:"";s:17:"extension_message";s:0:"";}}}s:4:"user";O:5:"JUser":25:{s:9:"\0*\0isRoot";b:1;s:2:"id";s:2:"32";s:4:"name";s:16:"Wolfgang Gothier";s:8:"username";s:7:"bixxxxx";s:5:"email";s:20:"wolfgang@gothier.net";s:8:"password";s:65:"xxxxyyyyzzzzc2f7385b6885314d0a89:NXIGAcFNDQvnxxxxI9EPKAzfLIwMdSPc";s:14:"password_clear";s:0:"";s:8:"usertype";s:10:"deprecated";s:5:"block";s:1:"0";s:9:"sendEmail";s:1:"1";s:12:"registerDate";s:19:"2011-01-27 23:01:07";s:13:"lastvisitDate";s:19:"2012-07-17 22:58:54";s:10:"activation";s:0:"";s:6:"params";s:92:"{"admin_style":"","admin_language":"","language":"","editor":"","helpsite":"","timezone":""}";s:6:"groups";a:1:{i:8;s:1:"8";}s:5:"guest";i:0;s:10:"\0*\0_params";O:9:"JRegistry":1:{s:7:"\0*\0data";O:8:"stdClass":6:{s:11:"admin_style";s:0:"";s:14:"admin_language";s:0:"";s:8:"language";s:0:"";s:6:"editor";s:0:"";s:8:"helpsite";s:0:"";s:8:"timezone";s:0:"";}}s:14:"\0*\0_authGroups";a:2:{i:0;i:1;i:1;i:8;}s:14:"\0*\0_authLevels";a:4:{i:0;i:1;i:1;i:1;i:2;i:2;i:3;i:3;}s:15:"\0*\0_authActions";N;s:12:"\0*\0_errorMsg";N;s:10:"\0*\0_errors";a:0:{}s:3:"aid";i:0;s:13:"lastResetTime";s:19:"0000-00-00 00:00:00";s:10:"resetCount";s:1:"0";}s:13:"session.token";s:32:"acbeb985432eee568bbe6f92a82275d5";}', 32, 'bixxxxx', '');
v2.5.6 sql dumpCode:
INSERT INTO `LBA_session` (`session_id`, `client_id`, `guest`, `time`, `data`, `userid`, `username`, `usertype`) VALUES
('a7ad84c30d4cdd341b30c5e3ff48c4cb', 1, 1, '1342566033', '__default|a:8:{s:15:"session.counter";i:1;s:19:"session.timer.start";i:1342566033;s:18:"session.timer.last";i:1342566033;s:17:"session.timer.now";i:1342566033;s:22:"session.client.browser";s:74:"Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20100101 Firefox/13.0.1";s:8:"registry";O:9:"JRegistry":1:{s:7:"\0*\0data";O:8:"stdClass":0:{}}s:4:"user";O:5:"JUser":25:{s:9:"\0*\0isRoot";N;s:2:"id";i:0;s:4:"name";N;s:8:"username";N;s:5:"email";N;s:8:"password";N;s:14:"password_clear";s:0:"";s:8:"usertype";N;s:5:"block";N;s:9:"sendEmail";i:0;s:12:"registerDate";N;s:13:"lastvisitDate";N;s:10:"activation";N;s:6:"params";N;s:6:"groups";a:0:{}s:5:"guest";i:1;s:13:"lastResetTime";N;s:10:"resetCount";N;s:10:"\0*\0_params";O:9:"JRegistry":1:{s:7:"\0*\0data";O:8:"stdClass":0:{}}s:14:"\0*\0_authGroups";N;s:14:"\0*\0_authLevels";a:2:{i:0;i:1;i:1;i:1;}s:15:"\0*\0_authActions";N;s:12:"\0*\0_errorMsg";N;s:10:"\0*\0_errors";a:0:{}s:3:"aid";i:0;}s:13:"session.token";s:32:"0cbaa26a43aed79006c4c0311f843cca";}', 0, '', ''),
I will continue to log any issues.