iCal keeps prompting me for password

I have this problem too. It's only started in the past few days but now it's affecting all my calendars. I'm seeing the same error as you plus hundreds of copies of:

8/9/12 1:38:54.237 PM CalendarAgent[660]: Unexpected EOF, returning last token as fallback

The only way I could make it stop was to disable all delegated calendars and restart the app a couple of times. It's clearly either a bug in Mountain Lion or a Google issue, and I suspect ML: colleagues running 10.8 are experiencing this issue but those still on 10.7 are not.

I'm curious if Apple and/or Google are tweaking security policies following the Wired hack last week. I'm using two factor authentication, I wonder if anyone without two factor are seeing this issue?

I was having this issue and thought the same thing about 2 factor authentication. However, i have the problem using the old password sytel and the 2 factor authentication. The problem doesn't happen until i try to enable my delegage calendars.

Ok. So after it keeps asking me to re-enter my password in Calendar app, i thought maybe that the attempts were triggering Google to lock the account to protect it from attacks. I went to google and changed my google password, then used that new password in Calendar and its working again. Delegates refreshed and everything working correctly.

1. I was originally using old single factor. Starting getting the prompts to re-enter my password in iCal. Searched online on google groups and found someone saying that they turned on 2 factor authentication and that fixed it. I then turned on 2 factor auth, setup app specific passwords through google's account management site. I then put the new passwords into iCal but it didn't fix it. I then disabled 2 factor authentication. That didn't fix it either. I then changed my google password and put that password into iCal and it worked.
2. iCal and iOS don't support 2 factor authentication. You have to create app specific passwords through google account management and then use those passwords in OSX and iOS.
3. I use 1Password to generate all my passwords (i have different passwords for every site). They are over 32 characters long and a mix of numbers, letters and symbols.
4. In iCal i deleted the Google account and set it back up using the new master password i described in #1

I'm seeing exactly the same thing. The moment I add any Delegate calendars the password prompts begin. This only started last night for me (may be coincidence that I had just changed my password). Nothing I have tried works, so I just hope this is something on Google's end that is fixed with us simply waiting this out. It is annoying, but at least everything being synced means we have other options to access it and issues with Calendar don't compromise the data (and my iOS devices still sync properly without any hitches).

Same problem. Has someone contacted apple about this?

Same thing here, annoying. Going back to Google Calendar until Apple fix this!

Having the exact same problem here. Changing password did nothing.

I got the password prompt, too and also "error 302". I was not able to sync new events from iCal to Google. I force quit the process "CalendarAgent" using Activity Monitor, and now syncing seems to work. And I haven't seen the password prompt nor error messages yet (though Console is full of errors).

Quitting calendar agent worked for me as well...

Im also getting the same problem.

Ive tried deleting passwords through keychain, force stopping Caldav processes in Activities, and deleting and reinstalling Calendar accounts.

Im on 10.8 and using delegates (8).

Here's what I get:

8/13/12 5:01:17.479 PM CalendarAgent[59836]: [com.apple.calendar.store.log.caldav.queue] [Account refresh failed with error: Error Domain=CoreDAVHTTPStatusErrorDomain Code=401 "The operation couldn’t be completed. (CoreDAVHTTPStatusErrorDomain error 401.)" UserInfo=0x7fe89606d290 {AccountName=Google, CalDAVErrFromRefresh=YES, CoreDAVHTTPHeaders=<CFBasicHash 0x7fe8938b9e40 [0x7fff78720190]>{type = immutable dict, count = 10,

entries =>

0 : Case Insensitive Key: X-Content-Type-Options = <CFString 0x7fe893895e80 [0x7fff78720190]>{contents = "nosniff"}

1 : Case Insensitive Key: Content-Type = <CFString 0x7fe893895c80 [0x7fff78720190]>{contents = "text/html; charset=UTF-8"}

2 : Case Insensitive Key: Server = <CFString 0x7fe8938d3310 [0x7fff78720190]>{contents = "GSE"}

3 : Case Insensitive Key: Transfer-Encoding = <CFString 0x7fff78b9c6b8 [0x7fff78720190]>{contents = "Identity"}

6 : Case Insensitive Key: Date = <CFString 0x7fe8938e4080 [0x7fff78720190]>{contents = "Mon, 13 Aug 2012 16:01:17 GMT"}

7 : Case Insensitive Key: X-Frame-Options = <CFString 0x7fe8938c17c0 [0x7fff78720190]>{contents = "SAMEORIGIN"}

8 : Case Insensitive Key: X-XSS-Protection = <CFString 0x7fe896016b70 [0x7fff78720190]>{contents = "1; mode=block"}

9 : Case Insensitive Key: Www-Authenticate = <CFString 0x7fe8938e0630 [0x7fff78720190]>{contents = "BASIC realm="Google CalDAV""}

11 : Case Insensitive Key: Cache-Control = <CFString 0x7fe8938f1c60 [0x7fff78720190]>{contents = "private, max-age=0"}

12 : Case Insensitive Key: Expires = <CFString 0x7fe896002560 [0x7fff78720190]>{contents = "Mon, 13 Aug 2012 16:01:17 GMT"}

}

}]