Contacts won't sync with iCloud?

So I just upgraded to Mountain Lion. However, none of my contacts are now listed in the Contacts app. Everytime I try to sync with iCloud, it freezes and I end up having to force close it after inifinitely waiting for the endless rainbow pinwheel of doom. Attempting to manually add or import a contact results in the same problem. In addition, when I switched the default sync to "This computer" (or whatever equivalent), I got this error message:

[NSInvalidArgumentException] *** setObjectForKey: object cannot be nil (key: /1342774233/carddavhome/card/)

Anyone know what to do? I'm about to ask for a refund for Mountain Lion and downgrade back to Lion. Thanks!