> However, HTTrack fails downloading the website.
> (http://tinyurl.com/kpw3dd)
> 
> Is it because of the filetype?> 
> I added +*.sss in the Filter Section in HTTrack, but
> that doesn't solved my problem.

The file extention is irrelevent. Some sites don't have any extentions (and
that is the proper way, url's don't change even if you change from cgi to asp
to jsp, etc)
Adding +*.sss does nothing since you didn't filter anything out and the link
is local.

The first page contains:
	<meta name="robots" content="nofollow" />
and the log states Startseite.sss" is set external

set options -> spider -> spider=no robots.txt