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 ('c5858ab6d759078500e34d2166d18cc7', -1, 1409683698, 1409683698, '17141383', 0, 0, 0)

Line : 373
File : sessions.php