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 ('6f32bd2b766c7ccbfd1e8ff7f7a8a0d5', -1, 1540139660, 1540139660, '36e0387e', -4, 0, 0)

Line : 187
File : sessions.php