Duplicate iCal Items after 10.6.3 Update

Question

After the latest software update to Mac OS X (10.6.3), I get duplicate items for everything in iCal (birthdays, holidays, events, etc). Anyone else having this problem and how do I delete all of the duplicates?

Answer 1

Days like this really make me question whether the Mac is indeed superior to Windows.
I've spent the last 4 hours recovering my calendars from this sync catastrophe. I keep about a dozen calendars in iCal (some are my own, others are subscriptions, a couple are CalDAV two-way links with Google Calendar). All of the calendars were replicated multiple times in iCal and on MobileMe - I had in excess of 150 items in my calendars list.
Some comments on how I've restored things so that hopefully others will not waste as much time as I have.
* First, shut off MobileMe sync. I don't plan on ever synchronizing my calendars through Apple services again. After previous troubles culminating in the current disaster, I don't believe this product is salvageable.
* Might be wise to disconnect from the Internet entirely while conducting surgery on your calendars. Several times, iCal somehow reconstructed files that I had explicitly deleted.
* Quit out of iCal before doing anything.
iCal files are in ~/Library/Calendars.
Delete the cache file in ~/Library/Calendars/Calendar Cache; also ~/Library/Caches/com.apple.iCal.
You need to use the command line for this.
Make a backup copy of your Calendars folder before following any of these instructions.
Each calendar is stored in a subfolder under ~/Library/Calendars. These folders are named with unique identifiers, like "F16776B1-14B9-428C-B6C9-4D240D894B3B.calendar". CalDAV subscriptions end with .caldav.
In each calendar folder there is an Info.plist file. Look at one of these files, towards the bottom you'll see: will include:
<key>Title</key>
<string>[CALENDAR TITLE HERE]</string>
Since we have replicated calendars, there will be many folders for calendars with the same title. So, given a calendar that you want to recover...
$ cd ~/Library/Calendars
$ CALS=`grep "CALENDAR TITLE" *.calendar/Info.plist|sed 's/\/.*//'|sort|uniq`
$ for x in $CALS; do echo $x; ls -l $x/Events | wc; done
You'll get a list of calendar folders with the number of events in each calendar.
One of these folders is the one you want to keep. Probably the one that has the most events. If there are several with the same number of events, they are probably all identical copies, so just pick one.
DELETE all the other folders except the one you want to keep.
Repeat the process for every other unique calendar.
When you're done, the number of .calendar folders in ~/Library/Calendars should be reasonable (in my case).
Check again that there are no cache files left in the ~/Library/Calendars folder.
Your calendars should now be repaired. Make another backup copy of the entire Calendars folder - because iCal has a tendency to "fix" things of its own accord, so the pollution could magically reappear later.
Start iCal. Things should be back to normal.
Watch out for mysterious processes called iCalExternalSync and Mingler consuming lots of CPU. I suspect that these are responsible for some of the calendar destruction insanity but I haven't caught them red-handed yet.
Good luck!