Dear list, we are running an OSX lion server and using caldav on it. Server: System Version: 10.7.4 (Build 11E53) Kernel: Darwin 11.4.0 Services: Mail, Open Directory, iCal Clients are running OSX 10.7.x and 10.8.x We had problems in the past with errors when refreshing calendars. It happened often that an error message 500 was shown when refreshing, especially if the user had more calendar delegations configured. After a long journey with the the apple support a workaround was mentioned to change the port from 'auto' to '8443' in the server settings for iCal on the client machines. We also changed the refresh rate for calendars from push to a fixed value. It seems that these changes solved the problems with the 500 error. Now we are facing a new error when receiving calendar invites as a attached ics file, mainly from outside our organization. When opening the attached ics file, an error 403 is shown and it is not possible to accept the invite. Contacting Apple support again was not successful because they are saying it is a different error and we need to purchase a new support case to get help from them. So the question is, can anybody give us a hint on how to solve these issue? Maybe someone already has a fix or a workaround for this error? If you need any further information, please let me know. Any help would be appreciated. Best Regards Frank