I'm unable to sync contacts because of an error "pushing data" to my iPhone, what can I do?

If you're having a problem syncing your contacts to/from your iPhone and are receiving a message that indicates an error occured while pushing data to the iPhone, here is a possible fix:

On Mac:

Open Finder and run iSync from the Applications directory. Select Preferences from the iSync menu and hit the "reset sync history" button.

Open iTunes and choose Edit -> Preferences. Select the Sync tab and choose to reset sync history.

This has been shown to resolve the "pushing data" error for most people.