phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO forum_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('791e0c57f96debb25645ddcab4db5ec8', -1, 1540147408, 1540147408, '3691534f', 2, 0, 0)

Line : 187
File : sessions.php