i am trying to sync my iphone 6s to my computer (it has the latest version of windows installed) and when i try to do it, it says it cannot be synced because an unknown error occoured (-54). please help!

If you are having trouble syncing your iPhone, iPod, or iPad after the Windows 10 update, don't worry. With just a few clicks you will be back up and running, and able to sync your device with your computer again. It appears as though the Windows 10 update is marking the iTunes folder as Read Only, meaning that your computer won't allow it to sync with the device you have plugged in. So, how do you fix this -54 error? Simple.

1. Open Windows Explorer
2. Head to the Music folder
3. Right click on your iTunes folder
4. Go to Properties
5. Uncheck the Read Only option under Atrributes

You will notice another pop up window as it applies the changes to all the sub-folders. If the problem still persists, verify that you have full control over the iTunes folder. To do this, right click the folder again, go to properties, then security, and finally click edit and then full control and apply. Once this is done, you should be able to head back into iTunes and sync your device again without an issue.

http://www.imore.com/having-trouble-syncing-itunes-after-updating-windows-10-her es-your-fix