It works now. although it doesn't explain why exactly it did not work previously.
It may have been due to wrong settings in the http.conf file but I tried it previously also with XITAMI instead of Apache and Xitami showed the same symptoms, hence I doubt is is http.conf related.
What I did do different this time is, I used the username and password (i-doit) during the setup. In my previous installation I used different usernames and password.