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 ('55b9a44c24ab0bb4afc045488b0249ad', -1, 1539760821, 1539760821, '36a285de', 15, 0, 0)

Line : 187
File : sessions.php