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 ('00c9a29a60b8543c7120bb3d81ef9e4f', -1, 1498156795, 1498156795, '36a16a51', 1, 0, 0)

Line : 189
File : sessions.php