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, session_admin) VALUES ('64abde4fe1fef6592457a654d0c96643', -1, 1397697154, 1397697154, '6ca2d22a', 23, 0, 0)

Line : 187
File : sessions.php