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 ('a18ce33737fb403c4f70652ec6fc9863', -1, 1397653488, 1397653488, '6ca2d26f', -4, 0, 0)

Line : 187
File : sessions.php