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 ('c8c435ef50238f28e89c6e84e0f5b9b7', -1, 1539978814, 1539978814, '36e0f72a', 7, 0, 0)

Line : 187
File : sessions.php