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 ('8d278f96497d459e2cf3f3e49a147d9f', -1, 1540054863, 1540054863, '36e0387e', -9, 0, 0)

Line : 187
File : sessions.php