iCal and Google Cal Error

frustrating error in ical. The Google calendar is syncing to iCal but this error continues to pop up every minute. How can I get rid of it?? My Mac is up to date! (fyi:I replaced my real ID with "username")

https://calendar.google.com/calendar/dav/username@gmail.com/user///calendar.google.com/calendar/dav/username@gmail.com/user/ is not a location that supports this request.