Can not access local web sites

Hi,

on my Mac Mini running Lion I cannot access any local web site

Normally, entering

http://localhost/~shortname/

would ad least show the index.html page located in the sites (Websites on German systems) folder, which I still can display w/o the webserver running by clicking on it)

However, I get the error message:

"you don't have permission to access /~shortname/ on this server"

This happens in Mountain Lion too, where I started the web server using the Web Sharing preference pane from

http://clickontyler.com/blog/2012/02/web-sharing-mountain-lion/

Any idea? I need this badly, because I am doing some little web dev

Thank you