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 ('a2b40ad2992b8ee8c1a975598f0f1cb8', -1, 1519026221, 1519026221, '36a71dd0', 52, 0, 0)

Line : 187
File : sessions.php