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 ('a675b333d8fc5bf7d88b1b104a7df71b', -1, 1540232935, 1540232935, '36c41a01', -8, 0, 0)

Line : 187
File : sessions.php