I just updated one of my projects (<https://www.frank-thomsen.eu/>) I manage to Drupal 7.50 and after that I get all the time an 403 error like that

> 
> Forbidden
> 
> 
> You don't have permission to access / on this server. Server unable to
>  read htaccess file, denying access to be safe
> 
> 
> Additionally, a 403 Forbidden error was encountered while trying to
>  use an ErrorDocument to handle the request.
> 
> 
> 

when I use 644 or 744 on every file and an 500 error, when I change the .htaccess to 755.

I have tryed to use a backup. Nothing! 

So also the Login-Page doesn't work. And like I said I cannot find the error! 
A test-page in a subdirectory works -> <https://www.frank-thomsen.eu/test/hhvm_test.php>

So, what could it be?

Greetings and best wishes!