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 ('3c12b4410148c9a8591f24ff713e1e8d', -1, 1462505378, 1462505378, '3652452a', -4, 0, 0)

Line : 188
File : sessions.php