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 ('79a8e56f3d7555e129b827eb743d2565', -1, 1398056193, 1398056193, 'b8495755', 2, 0)

Line : 158
File : sessions.php