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 ('7323a28a984f7910c0ec6fcf28ef9d04', -1, 1472386156, 1472386156, '36c6b7d9', -1, 0, 0)

Line : 187
File : sessions.php