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 ('f8b0b11282abd63b6a19bc39ca3731b7', -1, 1397727264, 1397727264, '6ca2d456', -4, 0, 0)

Line : 187
File : sessions.php