The advice here did not solve my problem, but I did figure out a way to make this work (from another Apple Support forum post).
I needed to get into iCal the calendar of a business partner. I have it set up to access easily in Google Calendar, but wanted it in iCal for convenience.
I had been trying to subscribe without success, following the instructions on this page to use the private ICAL link I had copied from the Google calendar. I kept getting an error saying there was no calendar available at that address.
The solution was to go to the Google Calendar Sync Settings page:
https://www.google.com/calendar/syncselect
On the syncselect page, I checked the box to enable that calendar for syncing, and then iCal sync with that calendar worked like a charm.
Explanation: My iCal was already connecting to my Gmail account successfully. It synchronized both ways very nicely (my calendar items can be created or updated in either iCal or in Google Calendar, and they appear and update in the other one). The trick was telling Google that I wanted to ALSO sync this "guest" calendar, using the checkbox on the syncselect page.
I hope this is helpful to someone else who runs into this challenge.
BTW - I am on Lion 10.7, but will soon be upgrading to Mavericks - I hope it works there too!
Eric Bobrow
http://www.bobrow.com