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 ('2ee9303913b2ab1bb649dffab0e4bebc', -1, 1537652014, 1537652014, '36e0a68d', 7, 0, 0)

Line : 187
File : sessions.php