If you’ve installed XCode 3.2.6 or 4.0 recently after previously installing iTunes 10.2.1 you may have seen this message when trying to sync: “iTunes was unable to load data class information from Sync Services. Reconnect or try again later.”

To fix this problem you’ll need to reinstall iTunes. Download iTunes from Apple, run the pkg, restart, and it should be fixed. Irritating, but at least there’s an easy resolution.