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 ('931bc4a545e2f37dfa96070724b5a617', -1, 1540120211, 1540120211, '36a174e1', 15, 0, 0)

Line : 187
File : sessions.php