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 ('4977f9531c5c2bf8c7a3bb53664c78b2', -1, 1397697129, 1397697129, '6ca2d22a', 23, 0, 0)

Line : 187
File : sessions.php