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 ('0a6f710ebcd32ecfa499a50a8ddc07ab', -1, 1283492146, 1283492146, '266bbf67', -8, 0, 0)

Line : 172
File : sessions.php