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, session_admin) VALUES ('eefa752b15e670bba80554ef52aa4993', -1, 1413851342, 1413851342, '365af3cc', -1, 0, 0)

Line : 187
File : sessions.php