Question display bug statistic black arrow

Hi,
I updated to kunena 1.5.6 from 1.5.5, and still have a problem, in place of black arrow, it is written : 'ascendind" and "descending" ? I installed the original kunena version.
How to fix and solve this problem please ? It's the same with Firefox and Internet Explorer... I am the only one to have this problem ? See the image attachment.
Thanks

This is the bug and the image attachment from Firefox.
Could you help me to solve this problem please, it's urgent !
Thanks in advance

Joomla installer corrupts sometimes files, so installing from tar, tar.gz, or bz2 may help to solve the problem.

Hi, thanks for your answer,
I looked and files up.gif and down.gif exists, I replaced them a second time, but I still have the same problem. How to know if files are corrupt ?
So you think I need tu unistall kunena 1.5.6 and replace it by a kunena.tar, tar.gz should fix this problem ?

I remember that in my first installation of kunena 1.5.5, after installing it I had patched it with a french version SFK 3.2.30, so it could come from this, perhaps there is a conflict ?

Hi, I think I found the problem origin, it come from my .htaccess.
I uninstalled and re-install a french kunena SFK 3.4 tar.gz version, but yesterday it was exactly the same with original kunena 1.5.6.zip version, when I uninstall and re-install kunena, I deleted my htaccess because it gives me right error and the back arrow are back. But when I put back my htaccess, they disappear again, so I think I need to comment a line or a caracter in my htaccess. I joined it on attacment, please could you look at it and try to help me to find which line or wich caracter is going wrong with kunena ?
Thanks in advance,
Best Regards,
david ;