Please reinstall your mini client by using the following link:
http://img.oasgames.com/upload/1468827100/NarutoOnline_en_2.3.0.7181_oas.exe
If it still doesn't work. Please leave your information in the following Thread:
http://forum.naruto.oasgames.com/en/forum.php?mod=viewthread&tid=222&extra=page%3D1