Persistent carddav error

I am getting the following frequent and persistent error in system.log:

Jun 18 18:42:04 xxx.yyy.com AddressBookSourceSync[71868]: [CardDAVPlugin-ERROR] -getPrincipalInfo:[_controller supportsRequestCompressionAtURL:https://SharedClientContacts@xxx.yyy.com:8443/principals/__uids__/B4F046A7-4C9D- 42EA-846B-825B39043D0E///SharedClientContacts@xxx.yyy.com:8443/principals/__uids__/B4F046A7-4C9D-42EA-846B-825B39043D0E/] Error Domain=CoreDAVHTTPStatusErrorDomain Code=401 "The operation couldn\u2019t be completed. (CoreDAVHTTPStatusErrorDomain error 401.)" UserInfo=0x7f8a14b08d40 {CoreDAVHTTPHeaders=<CFBasicHash 0x7f8a14b087f0 [0x7fff77f36f00]>{type = immutable dict, count = 7,

entries =>

0 : Server = <CFString 0x7f8a13562060 [0x7fff77f36f00]>{contents = "Twisted/12.2.0 TwistedWeb/9.0.0"}

1 : Content-Type = <CFString 0x7f8a1352a650 [0x7fff77f36f00]>{contents = "text/html;charset=utf-8"}

3 : Strict-Transport-Security = <CFString 0x7f8a1351ec10 [0x7fff77f36f00]>{contents = "max-age=604800"}

6 : Date = <CFString 0x7f8a1352a620 [0x7fff77f36f00]>{contents = "Thu, 18 Jun 2015 22:42:04 GMT"}

9 : Www-Authenticate = <CFString 0x7f8a1353cfe0 [0x7fff77f36f00]>{contents = "digest nonce="9221e36f3a61b5e246eab75a", algorithm="md5", opaque="54fc94cbe5a9d294427759a966efc45f-OTIyMWUzNmYzYTYxYjVlMjQ2ZWFiNzVhLDE5Mi 4xNjguMTM3LjY3LDE0MzQ2NjczMjQ=", realm="xxx.yyy.com", basic realm="xxx.yyy.com""}

10 : Content-Length = <CFString 0x7f8a135620a0 [0x7fff77f36f00]>{contents = "141"}

12 : Connection = <CFString 0x7f8a1351e050 [0x7fff77f36f00]>{contents = "close"}

}

The account referenced in the error, "SharedClientContacts", was deleted a couple of years ago, using WGM. Also, xxx.yyy.com is a placeholder for the real name.

Can anyone explain what's going on here?