Currently Being ModeratedJul 25, 2012 12:55 PM (in response to reeeves)
I'm having the same problem. Contacts appear on the iCloud website, but I cannot add a contact to the Contacts application using a vcard downloaded from iCloud, or by creating a new contact card in the application. When trying to sync with iCloud it displays the error message:
[NSInvalidArgumentException] *** setObjectForKey: object cannot be nil (key: /121455241/carddavhome/card/)
Currently Being ModeratedJul 25, 2012 1:58 PM (in response to reeeves)
I'm also having the same problem. Contacts are visible on iCloud but nothing is displayed within the Contacts application. I've tried disabling/re-enabling iCloud Contacts and when I try and import anything from a downloaded vCard it realises it's a duplicate but still does not display. I'm finding that Contacts is running very slowly as do other applications when they try and access Contacts (such as Mail when you try and address a new email...)
Currently Being ModeratedJul 25, 2012 2:08 PM (in response to reeeves)
I've managed to find a solution with whatever had been going wrong (in my case, at least). Follow the instructions marked "For issues syncing contacts and contact groups in Address Book", with the Lion instructions on this KB article:
Hope this helps!
Currently Being ModeratedJul 26, 2012 7:16 AM (in response to reeeves)
This seems to be a somewhat common problem when going from Lion to Mountain Lion and storing contacts in Apple's Cloud.
I've seen the same complaint on two other forums.
But the steps listed in the Apple article above may be overkill.
Referencing the Apple article for file locations, others are saying all that's required is to delete the Address Book folder in the Applications Support folder and then restart the Contacts app. Another person said what worked for him was to trash the the same Address Book folder and the two Prefs files.
If I had this problem, I'd start by deleting only the Address Book folder and see if that works. That's drop dead easy to do and quick.
It's not like you're going to lose anything by trying. Everyone has said their contacts are still intact when going to iCloud.com so it's an access problem. You can confirm that by signing on as a different user and opening the Contacts application (and entering the correct Apple ID info of course).