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 ('593d4dfc0dc7d3dbe7759c4aa5288bc0', -1, 1529873367, 1529873367, '36e05bf6', -9, 0, 0)

Line : 187
File : sessions.php