phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in) VALUES ('9a76e9f8255aafdb259eed24547a205c', -1, 1409692450, 1409692450, '36a66ede', -9, 0)

Line : 158
File : /forum/includes/sessions.php