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 ('b5f7c4ddf3f0bfb8ce856d8a21c7bf7e', -1, 1529637844, 1529637844, '36a2a59e', 2, 0, 0)

Line : 187
File : sessions.php