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 ('d213ccbe6ec951d69a7e7a7b6400d88d', -1, 1406703616, 1406703616, '36c5d792', 5, 0, 0)

Line : 189
File : sessions.php