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, session_admin) VALUES ('c8cacf97c4d32045fe39db420c7fa1e7', -1, 1397717166, 1397717166, '6ca2d4e2', -4, 0, 0)

Line : 187
File : sessions.php