The topic of this thread was happening under 10.5.6 as noted. That other thread is unrelated except that it describes why I didn't want to upgrade my Macs to 10.5.7.
Now that ZCS 5.0.18 has fixed bug 38112 I've upgraded all my Macs to 10.5.7. Since the ZCS to 5.0.18 upgrade I haven't seen this CalDAV error, so it's possible the server upgrade solved the problem, but it's a bit early to say.
If I was trying to reproduce the error I'd try messing with the calendar (or a single appointment) via the web interface and iCal simultaneously. |