[Solved] Can't login to CB, joomla core login appears

Hello Joomla! community,

I am using Community Builder 1.8.1 and Joomla 2.5.7.

Now my login page shows

Duplicate entry '' for key 'PRIMARY' SQL=INSERT INTO `xxxx_session` (`session_id`, `client_id`, `time`) VALUES ('', 0, '1351260548')

It also redirects me to Joomla core login page and when I click on login page, it doesn't go anywhere.

Is there any solution?

Thanks in advance.

Finally I solved the problem by restoring changed files edited to disable cookies for guest, explained in this guide . The problem came after updating to 2.5.7. There was no problem when using 2.5.6.

Now I have to look for other ways to disable cookies for guests.