Update: Eradiction of this error proved impossible. Upgrading to Mountain Lion largely ameliorates the problem.
Because I eschew iCloud, rather hoping it will go away, I still use Google Calendar and iCal. This marriage used to require Calabaration, but is natively supported in more recent versions of iCal. However, although multiple calendars are handled gracefully for the initial account acquisition, later on, multiple copies of events can appear, and creating events can fail with this message:
The server responded with an error.https://calendar.google.com/calendar/dav/%5Bmyname%5D@gmail.com/user/ is not a location that supports this request.
Later, the event will pop up again in the “wrong” calendar, and will keep doing so. In this case, a solution that worked on my Macbook is to delete the calendars from your local machine and clear the iCal cache. Adding the calendars back again is much less strife than it used to be, and then things went back to normal. However, on my work iMac this didn’t take. I searched again for answers and found a very quick and strange fix. Deleting the calendars in iCal and adding them back through the “Mail, Contacts & Calendars” pane on the System Preferences (which actually amounted to just clicking a check box next to the Google – inactive entry) made all the pain go away.