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 ('35c73f58da0d5444829aa75f30b4e0e0', -1, 1540034571, 1540034571, '36e11a2c', -4, 0, 0)

Line : 187
File : sessions.php