I had this error too.
I did following:
1.) I have deleted in iCal and in Systemsettings the accounts of GOOGLE
2.) I exited iCal and Systemsettings
3.) I started SCHLÜSSELBUND and searched for "GOOGLE" or "GOO" and "DAV" or "CALDAV" and "GMAIL" and deleted ALL KEYS connected with.
4.) I started Safari and GOOGLE-Account (with STAY-SIGNED IN = NO) and I then changed SIGNIN-PASSWORD in GOOGLE - not the same PASSWORD AS BEFORE
5.) I exited GOOGLE AND SAFARI
6.) In Systemsettings I have made a new GOOGLE ACCOUNT under "Email, Contacts ..."
7.) In iCAL-settings I have then made a new GOOGLE ACCOUNT and entered the NEW PASSWORD
8.)
IMPORTANT:
in GOOGLE I too have SUBSTITUTES. And after building a new ACCOUNT in iCAL
VERY IMPORTANT:
I did NOT ACTIVATE SUBSTITUTES but only my GOOGLE MAIL ADDRESS!!
9.) GOOGLE SUBSTITUTES I have UPDATED in iCAL on NEXT working day! I did let GOOGLE SERVER time to update all calendar substitutes.
10.) IMPORTANT: I did set UPDATING iCAL to EVERY 15 MINUTES - This because in Windows and LIVE-Mail I got errors on updating emails every 1 MINUTE - error said this is too fast to be updated and server could not be reached so shortly.
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That's it! It my help You too. Try it.
Yours, Gerhard
System:
OS X Version 10.8
iCAL Version 6.0 (1639)