I upgraded one of my Macs to OS X Mountain Lion. Today, I found out, that iCal communication has changed. I cannot enter nor modify calendar entries which are hosted on a Zimbra server and accessed through the CalDAV protocol. - The same calendar can be updated from a 10.7 OS X Client without any problem.

So it seems that Mountain Lion changed the way of its communication to CalDAV servers. I get the following error message in iCal: The server responded with “400” to operation CalDAVWriteEntityQueueableOperation.

In the trace.log, I can see the following entry:

15:44:46.256:btpool0-9361://my.server.com/dav/user%40server.com/Calendar/02E2EF91-CA7D-4122-84C7-7AB6E3A32F69.ics PUT null; Mac OS X/10.8 (12A269) CalendarAgent/47
15:44:46.256:btpool0-9361://my.server.com/dav/user%40server.com/Calendar/02E2EF91-CA7D-4122-84C7-7AB6E3A32F69.ics 401 null 0
15:44:46.312:btpool0-9361://my.server.com/dav/user%40server.com/Calendar/02E2EF91-CA7D-4122-84C7-7AB6E3A32F69.ics PUT null; Mac OS X/10.8 (12A269) CalendarAgent/47
15:44:46.318:btpool0-9361://my.server.com/dav/user%40server.com/Calendar/02E2EF91-CA7D-4122-84C7-7AB6E3A32F69.ics 400 null 0

Any idea if this can be fixed somehow?