Have been using iCal as the primary source for our families calendars for several years now and have multiple calendars (School, Work, Bills etc.) and had been using the CalDav method of syncing the two calendars prior to upgrading to iCal 5.X with. Currently running version 5.0.3 of iCal and version 10.7.5 of OSX. Recently (for about 2 months now) iCal has been throwing the attached error message... This happens most of the time when on iCal an existing item is changed from one calendar to another, for example. Water Bill due on 1/23 is on Calendar Bills Due. After paying the bill the event is changed to Bills Paid. The error pop up gives two options Go Offline and Revert to server. I have tried removing all the accounts from iCal and going through the process of reconnecting the Google account, but the errors still occur, and sometimes the errors pop up when the calendar updates with out making changes in iCal. Upon clearing iCal and reconnecting to Google, all of the events pull down from Google with out a problem, and I can add a new event no problem, but if I don't want it on the default calendar and change it I get the error. My wife and I both have Android powered phones and the go between of Google Calendar allows for us to update the Calendars on the go and keep iCal at home up-to-date as well. Any help would be appreciated.