phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO ultramtramadol_phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin, is_robot) VALUES ('8025e3995f2a6ef033e8e912c72f986b', -1, 1513490432, 1513490432, '36dd883e', 0, 0, '0', '0')

Line : 175
File : sessions.php