I get this error message when I receive a event invitation per email (and mail automatically tries to add it to iCal). I've setup a CalDAV account with fruux, and have one normal calendar there (which is set as the default calendar for iCal to add new events to). The Task calendar (for the reminders is set as the default calendar for new Reminders).
But somehow iCal want's to add the news invitation to the "Tasks" calendar instead of my "Private" calendar. The error message I get is the following (excuse the german):
Der Zugriff auf „23.02.13: Title of Event“ in „Tasks“ im Account „fruux“ ist nicht gestattet.
Antwort des Servers: „403“ an Vorgang CalDAVWriteEntityQueueableOperation
I've read some threads with a similar issue with iCloud but their have not the same error message as I get. And the solution proposed there does not help me. The solution was to have different names for the normal calendar and for the reminder calendar, which I already have.