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 ('a4dc0d771989e2679ee0f4eb6d3c66c2', -1, 1506313971, 1506313971, '36e0d65d', 2, 0, 0)

Line : 187
File : sessions.php