phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('eaedc323f2b1d442c2fff454a5ff3c80', -1, 1412145996, 1412145996, '3659467c', -1, 0, 0)

Line : 187
File : sessions.php