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 ('2ac166f9183b329225e82a4b96d96859', -1, 1397644011, 1397644011, '6ca2d4f5', -4, 0, 0)

Line : 187
File : sessions.php