Allowing the Synchronization Client to see the iTunes Library
Problem Description
The synchronization client cannot see the iTunes library.
Possible Cause #1 and Resolution
After iTunes 12.2, the iTunes library is not shared in a way third parties can read it without some additional configuration. To enable this functionality:
Open iTunes preferences.
Select the Advanced tab
Check the Share iTunes Library XML with other applications checkbox
Restart the Synchronization client
For more information, please see Apple's article on the issue here: https://support.apple.com/en-us/HT201610