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 ('11a1785d674b9d18f25792fa1627d3ed', -1, 1406710913, 1406710913, '365abc07', 79, 0, 0)

Line : 180
File : sessions.php