"The iPhone [device name] Could not be synced because the sync session failed to start"
Several work-arounds have been suggested including simply restarting the iOS device. One procedure that seems to work well is to remove the device backups from iTunes. Before you do this, make sure you backup your backups folder: ~/Library/Application Support/MobileSync/Backup/
- Connect your device and open iTunes
- Go to Preferences/Devices
- Delete all backups
- Click "OK"
- Restart iTunes and attempt another sync
Apple's iOS troubleshooting page has some good tips: http://support.apple.com/kb/ts2529