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 ('9e66b9ca7ac9b3eefef45b54117f1d70', -1, 1540128737, 1540128737, '369c27f5', 7, 0, 0)

Line : 187
File : sessions.php