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 ('c2778ed0b616e382823283f49493cae4', -1, 1409209458, 1409209458, '3653e26d', -1, 0, 0)

Line : 187
File : sessions.php