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 ('eb9b330f132474267942cdc67db79dd7', -1, 1406574284, 1406574284, '36c5d792', 2, 0, 0)

Line : 187
File : sessions.php