Mavericks Calendar Google error message 404

In the last day or two I'm getting an error message stating something like "the URL https://calendar.google.com/calendar/dav/xxxxxxxxxxxxxxxx/user/ encountered HTTP error 404. Make sure the URL is correct." every time I try to do something in the Mavericks calendar app. The calendar is still synching correctly though so why is the irritating message suddenly appearing for no reason?