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 ('65a64da3dc4d1b132e843ac3f155bfb3', -1, 1406229684, 1406229684, '36c4c39e', 12, 0, 0)

Line : 180
File : sessions.php