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 ('940353db4b83c785023e266158770102', -1, 1529879191, 1529879191, '36c69e18', 28, 0, 0)

Line : 187
File : sessions.php