Did you try the troublshooting mentioned here? Troubleshooting iPhone and iPod touch contact and calendar syncing via USB on Windows
Start with resetting the sync history:
If you find that some of your data syncs to your device but you see an unexpected number of changes or modifications, you may need to reset your sync history. This causes iTunes to prompt to Merge or Replace information on the device when you next attempt to sync your information. To reset your Sync History:
- Open iTunes.
- From the Edit menu, choose Preferences.
- Click the Devices tab.
- Click the Reset Sync History button.