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 ('e78c0653bcb40c60954b1126cf4e5e0c', -1, 1469793508, 1469793508, '36a139b1', -1, 0, 0)

Line : 187
File : sessions.php