Address Book no longer syncs to iPhone

Question

I'm running Snow Leopard (10.6.8) on my MacBook, which uses iTunes 10.5.1. My iPhone 3GS is running iOS 5.0.1. I use the OS X Address Book application to manage my contacts. Recently, I noticed that changes were no longer being synched between my MacBook and my iPhone. Other information (such as calendar info) was being synched fine.
I tried to fix this in the following ways:
- Configured iTunes to "Replace information on this iPhone" for contacts (under iTunes' Info tab).
- Reset sync history in iSync.
Neither of these things fixed the problem. The odd thing is that iTunes displays "syncing contacts" for 8-9 seconds every time I sync my iPhone (I have a lot of contacts). So it *seems* as if the contacts info does actually get exchanged between the Mac and the phone. But when I open the Contacts app on my iPhone, it displays "no contacts".
Last week, I got a new, larger hard drive for my MacBook. I installed Snow Leopard on the clean drive and restored my backups, including contacts. In order to make sure everything was really clean, I wiped my iPhone too. Then I tried syncing them. Contacts STILL did not appear on the iPhone. At the time of the first sync, I had no additional software installed on my Mac -- it was just a clean install of OS X with Apple's updates (of OS X and iTunes) applied. Even now, I have only a few additional applications installed (LibreOffice, Audacity, Firefox, Chrome, Opera).
The fact that the problem has persisted even after the reinstallation suggests to me that the problem might be with the contact data itself. But my contacts look fine on the Mac.
Can anyone suggest a possible next step?

Answer 1

OK -- problem solved. Here's what I did:
1. Opened the Address Book application.
2. Highlighted all my contacts and dragged them into a new directory that I created under Documents. This created a single vcard file containing all the contacts.
3. Shut down (i.e., File/Close) the Address Book application.
4. Went to ~/library/Application Support/  and renamed the AddressBook directory to AddressBook.bak (so that the Address Book application would no longer find the directory).
5. Opened the Address Book application. It automatically created a AddressBook directory and a new address database containing only the two default addresses (Apple and my own address).
6. Dragged the vcard that I created in step 2 into the open Address Book application.
7. Confirmed that I wanted to import a large number of addresses.
8. When the import was done (about 15-20 seconds), connected my iPhone and did a sync.
Now I have all my contacts back in my iPhone again. But I have lost the group information that I created (business, personal, etc). This is not a big problem. Even if I have to create the groups and assign records to them manually, I can have it done in an hour or so, which is nothing compared to the time I have been wasting trying to get this problem fixed.