phpBB : Critical Error

Error creating new session

DEBUG MODE

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

INSERT INTO forum_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('a71c4b09c48e08af9a6a22b58db2de52', -1, 1540229374, 1540229374, '36e0f72a', 2, 0, 0)

Line : 187
File : sessions.php