after even more wrestling.... I got this to work too.. but with a few tweaks...
Firstly I deleted the calendar files as per here https://discussions.apple.com/thread/5641818 not sure whether this helped or not.... but I didn;t get it to work before and it was good to know there was no old files spoiling my chances.
Then I followed the instructions with a couple of tweaks/clarificaitons
After quite a bit of wrestling, i got it to work.
1. Go to the calendar application and create a new account.
2.Select "Add CalDAV Account".
3. Select "Account Type" as advanced.
4. Enter your username and password. *** I used only the part before the @ ***
5. Enter "Server Address " as google.com
6. Enter "Server Path"
***I used firstname.lastname@example.org/user on the end ******
7. Select "Use SSL" and port should be 443.
Then I it worked for me - woohooo... been struggling for days with this one !