after hours and hours I came to the conclusion, that xenforo somehow troubles redirecting with .htaccess.
In my xen, I have the following code in my htaccess, that leads www.myforum.com/index.html to a xen 404-page:
RewriteEngine On RewriteBase / RewriteRule index\.html index.php [L]
Where the hell do I have to configure xen to interprete the htaccess as it should be done?!
Thanks and best regards.