URL rewriting and htacces

Hello Everyone,

I just joined the PunBB community and installed my first forum on my server.
Everything was working smoothly until I switched the URL mode to "file (fancy)".

I think there are some changes to make this mode work and rewrite urls.
I have changed my .htaccess file to:

<IfModule mod_rewrite.c>
# MultiViews interfers with proper rewriting
Options -MultiViews

RewriteEngine On

# Uncomment and properly set the RewriteBase if the rewrite rules are not working properly
#RewriteBase /

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . rewrite.php [L]
</IfModule>

# END PunBB

But it doesnt seem to work. (forum adress: forum.mister-tablet.com)

Can someone help me please?
Thanks for your help!