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 ('764b4663c4e6757a6f3b1b10c7459158', -1, 1397674566, 1397674566, '6ca2d4f2', 23, 0, 0)

Line : 187
File : sessions.php