iCal issue with Mountain Lion

It's to do with the Default Alarm setting. There is a bug that does not allow "Alert" to be set to "None".

To temporarily solve this bug, set the default alarm for that account to anything other than "None". And also, don't change alert setting of any existing event to None.

Worked like a charm - great workaround! Hopefully Apple and Zimbra will work this out soon, but this got my calendar back on the air.

This fix did not work for me - it doesn't seem to have anything to do with creating events, I get an unspecified error when iCal attempts to even connect to the CalDav server now (keeps reprompting for PW and when I enter it, saying "The server responded with an error." with the same settings I had before, that worked fine as of last night on Snow Leopard, and that are still working fine on the iOS devices). I tried setting the default reminders so that none of them were "none" (which none of them were before anyway), but it still won't connect. Any ideas?

Apple, please help! This is a really huge, fundamental breakage for me.

Is there any way to back out the Mountain Lion install short of paving the machine and starting over?

Actually, to clarify, the problem is more fundamental for me - it's not just that I can't create or modify calendar entries, I cannot connect to the CalDAV server at all anymore.

Never mind, fixed this myself - turned out to be an old, unfixed bug in iCal relating to use of old keychain entries - see http://www.atpeaz.com/index.php/2011/fixing-lions-icals-caldav-password-problem/. After I removed the calendar, then removed all of keychain entries, then re-added the calendar, it came back to life and stopped giving login errors.

Set the default alarm in Zimbra or in Apple Calendar?

What worked for me was just deleting the calendar from iCal, deleting the bits associated with the calendar from Keychain, and re-adding the calendar to iCal. No more problems!

This workaround works for calendar entries with specific hours. The bug still exists for all-day events.

Yes, the fix works for both timed events and all day events. Set a default alarm for your Zimbra calendar from inside the Mac Calendar app in Preferences. Also, as mentioned the bug fix is ready to roll out in Zimbra Server 7.2.1, which is now available.

I will not ask, Why? I'll say - Bravo!!! 🙂

I solved this problem through System Preferences. First, I deleted the accounts in the Calendar preferences.

Then go to System Preferences, click on Mail, Contacts & Calendars. Select the account that you're having issues with. And make sure the "Calendars & Reminders" is checked. I checked this and that solved my issues.