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 ('8f88a1a1d2c4e0e5f13b9eb367db452a', -1, 1540116535, 1540116535, '36a174e1', 5, 0, 0)

Line : 187
File : sessions.php