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 ('093b66082b94d008136bf6fbe3a3269e', -1, 1462076011, 1462076011, '36a322ed', -1, 0, 0)

Line : 187
File : sessions.php