Reinstalled USB driver, installed iCloud for Windows: no change. Now syncing does not work via USB and WiFi, Sync button is greyed out and backup also does not work. But then I did the upgrades to iOS9 and iTunes 12.3.1. Never had a problem with an iTunes update. Syncing was never a problem with iTunes on WIndows 10 and my iPhones - now an iPhone 6. We need to make sure it's the iTunes version from Apple's website and not the one from the Microsoft Store. I have been running iTunes for Windows for years now. While iTunes is not a requirement to run Duet, it's likely some of the required drivers were not installed properly during Duet's installation process and iTunes can help with that. If you have problems using the iTunes Store on PC If you’re unable to browse, sign in to, or buy music from the iTunes Store in the iTunes app on your PC, try the following: If you see a message that your computer can’t connect to the iTunes Store, choose another item from the pop-up menu (Podcasts, for example), then click Store again.