Currently Being ModeratedMar 18, 2013 9:29 AM (in response to neuegestaltung)
iCal Server not running
This discussion helped me :-)
Stop "Calender Server" in Server App.
Open Terminal and enter the following command:
sudo rm /Library/Server/Calendar\ and\ Contacts/Data/memberships_cache
Start "Calender Server" again
View Error Log of Calender Server. It should contain this line:
Starting group membership cacher service
Use Network Utility from Utilities folder and run a port scan on 127.0.0.1.
Open Ports 8008, 8800, 8443 and 8843 should appear.