phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 2

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in) VALUES ('83510a32bf3f469c444b17b4cc80739a', -1, 1406813484, 1406813484, '36cdbd9c', 20, 0)

Line : 315
File : sessions.php