phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 2

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in) VALUES ('5516c669f80b90371a8eb04700355aab', -1, 1413979880, 1413979880, '36a70af4', 20, 0)

Line : 315
File : sessions.php