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 ('ac3a62a11ed4c80b0f005b6349ff1f6b', -1, 1466973707, 1466973707, '36c68a82', -1, 0, 0)

Line : 187
File : sessions.php