My use case is slightly different; we still use our google calendar inside "iCal", and we got the same error text.
Not sure whether this will solve it longer-term, but I simply deleted the Google account from Calendar / Accounts... and then re-added it. After ~20 minutes, the pop-up has not popped up, so I'm calling this 'success' for now.
- In Calendar on the Mac, choose Calendar / Accounts... ( this will open System Preferences / Internet Accounts )
- Find the Google account which is syncing its calendar to iCal
- Select it (click) and then remove it by clicking the minus icon [ - ] below the list of accounts. Read and confirm that you're removing the account. It's your choice.
- Close (quit) Calendar if you have not already closed it. This may not be necessary, but I quit the application just the same.
- Back in Internet Accounts, click the [+] to add a new account. Choose Google.
- Enter your Google account name and password. Choose Calendar and un-check any that you do not want.
- Re-open Calendar and the google calendars should re-sync and display as expected. If you chose any custom colors, you may need to reset them according to your preferences.
I hope this helps. Good luck!