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 ('eba3fd7eb7c3470caf50ca9426a8f6ff', -1, 1406343894, 1406343894, '3651ec24', 0, 0, 0)

Line : 373
File : sessions.php