Yes, i have monitored /var/log/apache2/error.log while acesing server/webapp and nothing is written to this file.
The error is not a browser error but a zarafa webapp error.
In the browser windows i get the zarafa icon, a red circle with white cross inside (Error icon) and the text "HTTP401 Unauthorized".
NEWS: While i was testing again and checking diferents log files, after 4 to 5 reloads of the webapp page i got the preferences page. I have filled the form and now i can access again. I have not fixed anything.....