Error 500 When I use Permanent Link

I am Vietnamese. When I use Permanent Default (EX: http://blog.ninja-net.info/?p=123), It works fine.
But when I use other Permantlinks type, when the title of post is written in english, it works fine too, but when the title is written by Full Vietnamese, error 500

Work Fine: http://blog.ninja-net.info/Favourite-music/
Error: http://blog.ninja-net.info/bai-viết-mới-nhất or http://blog.ninja-net.info/bai-vi%e1%ba%bft-m%e1%bb%9bi-nh%e1%ba%a5t/