[Thu Oct 27 09:41:02 2011] [error] [client 188.8.131.52] PHP Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/session) in
Please check whether you have this directory in place, create it if it hasn't there.
Change the permission to 777, and try run it again.
If you were able to see session files being written, then you are good.
Now make sure the file permission for those session files in this directory was not readable and writable by other users.
[root@server apache2]# ll /var/lib/php/session/
-rw------- 1 userb userb 40 Oct 27 09:39 sess_3bsrvlkc291l7jlsakvtknv3v0
-rw------- 1 usera usera 30 Oct 27 09:39 sess_3s95nd55qs44s0uslsai2ghlu7