phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('18574ddf5f1c92fbf1a3cabc7b647c4f', -1, 1529706829, 1529706829, '3651c518', 40, 0, 0)

Line : 187
File : sessions.php