Contatti OS X (Mountain Lion) con CardDav - "CoreDAVHTTPStatusErrorDomain error 500"

Ho recentemente configurato un account CardDav con un account Atmail Cloud ospitato. Funziona perfettamente su iOS e sembra inserire alcuni dei contatti, tuttavia ogni volta che i contatti vengono risincronizzati, ricevo il seguente errore:

    9/20/12 5:19:24.622 PM Contacts[785]: [CardDAVPlugin-ERROR] -_handleCompletedAction: Error Domain=CoreDAVHTTPStatusErrorDomain Code=500 "The operation couldn’t be completed. (CoreDAVHTTPStatusErrorDomain error 500.)" UserInfo=0x7ff1a6409cb0 {CoreDAVHTTPHeaders=<CFBasicHash 0x7ff1a61475b0 [0x7fff73a56fd0]>{type = immutable dict, count = 8,
entries =>
    0 : Case Insensitive Key: Server = <CFString 0x7ff1a66096c0 [0x7fff73a56fd0]>{contents = "Apache/2.2.15 (CentOS)"}
    1 : Case Insensitive Key: X-Powered-By = <CFString 0x7ff1a64bc030 [0x7fff73a56fd0]>{contents = "PHP/5.3.3"}
    2 : Case Insensitive Key: Connection = <CFString 0x7ff1a64aa4a0 [0x7fff73a56fd0]>{contents = "close"}
    3 : Case Insensitive Key: Content-Type = <CFString 0x7ff1a661ccb0 [0x7fff73a56fd0]>{contents = "application/xml; charset=utf-8"}
    6 : Case Insensitive Key: Date = <CFString 0x7ff1a4efb270 [0x7fff73a56fd0]>{contents = "Thu, 20 Sep 2012 21:19:24 GMT"}
    8 : Case Insensitive Key: Content-Encoding = <CFString 0x7ff1a64a7220 [0x7fff73a56fd0]>{contents = "gzip"}
    10 : Case Insensitive Key: Content-Length = <CFString 0x7ff1a6149f80 [0x7fff73a56fd0]>{contents = "187"}
    12 : Case Insensitive Key: Vary = <CFString 0x7ff1a665dd70 [0x7fff73a56fd0]>{contents = "Accept-Encoding"}
}
}

Si tratta di un problema con il server CardDav o Contatti? Qualcuno ha riscontrato questo problema in precedenza?