How can I get back Mail Auto-Complete email addresses?

Question

After upgrading to Mountain Lion, my Mail no longer works with the auto-complete of email address.
My Contacts.app works fine, it just seems that Mail is no longer able to 'read' from my Contacts.
I use iCloud and everything was great for years.  Mail preferences is set to Auto-Complete email address from my Contacts.
Not sure how the problem started, but I launched Mail on a 2nd computer  - on the same iCloud.
Shortly after I did that, my 1st Mac no longer auto-completes email.  I'm unsure if that is what set off the problem.
Also, I 'did' read Tom Nelson's article which did not work since it's not an 'alias' problem:
http://macs.about.com/od/MacTroubleshootingTips/qt/What-To-Do-When-Mountain-Lion -Mail-Fails-To-Auto-Complete-Email-Addresses.htm
Also, there doesn't appear to be a com.apple.mail.plist preferences file I can even delete in Mountain Lion.
I use Dropbox, but have never it to sync Addresses, Calendar, etc.
Any help greatly appreciated! 
-Mark

Answer 1

I had the same issue. After reading this solution I started poking around in the Container folder and found that there was a symlink for AddressBook that was messed up which was causing the problem. In ~/Library/Containers/com.apple.mail/Data/Library/Application Support I ran:
$ cd ~/Library/Containers/com.apple.mail/Data/Library/Application\ Support
$ ls -lh
AddressBook -> ??/???7??ʪ?????VT???;??\G[?:??:??????T?_Ү??
CrashReporter
Mail
SyncServices -> ../../../../../Application Support/SyncServices
iCloud -> ../../../../../Application Support/iCloud
Seeing the aliases for SyncServices and iCloud, I guessed correctly that I just needed to recreate the AddressBook alias to point to the right place. So I just removed the alias for AddressBook, recreated it, restarted Mail, and it worked perfectly. (Note: I did the following to remove the alias, and recreate it. You should confirm what you are removing is an alias. You should also always make sure you have a backup.)
$ cd ~/Library/Containers/com.apple.mail/Data/Library/Application\ Support
$ rm AddressBook
$ ln -s ../../../../../Application\ Support/AddressBook AddressBook
Obviously, DrewSchatt's  original solution to this works as well, but this way you don't have to delete the whole folder, resetting your preferences and possibly delete something else important (only recreating the alias, not deleting any files or data).