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 ('3d71d7da39fb0ddf5fdde79d8c565cdb', -1, 1406623187, 1406623187, '36e30b02', 42, 0, 0)

Line : 180
File : sessions.php