Home sharing on iPhone: "You don't have permission to access the requested resource "
Fix:


Sign out of Home sharing:  iOS Settings > Music > Sign out of Home Sharing
Sign in to Home sharing again, with your Apple ID.
Terminate the Music app. Double-click the Home button to bring up the iOS app switcher. Swipe the Music app with an upwards motion, to terminate it.
Open the Music app again. Home Sharing should now be working again. You will have to reindex the contents.


I don't know why this problem exists, but Home Sharing seems to have become increasingly unreliable as Apple post-Jobs appears to divert resources elsewhere.