According to the KB article, users experiencing problems see a “-50” error when attempting to sync content with iTunes from their iPhone, iPad or iPod touch.
Apple released iTunes 10.3 on Monday with support for the new Automatic Downloads feature that lets users purchase from the iTunes Store and App Store on one device and have the content download automatically to their other devices. It also added the ability to re-download previous purchases without paying again, and added the ability to purchase books from the iBookstore.
The iTunes 10.3.1 update is free and available via the Software Update application, or as a downloadable installer from the Apple Web site.