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 ('70b83b18b5e4b3d64d8d483a0c0a6b69', -1, 1544835542, 1544835542, '0350554c', 2, 0, 0)

Line : 187
File : sessions.php