Problem: Attempting to publish an app from Xamarin Studio to an iOS 8.x device fails. You may see various error messages about unable to write/find Manifest.plist, and you'll likely see an error message akin to AMDeviceSecureInstallApplicationBundle returned: 0xe8000097 (kAMDInstallProhibitedError).
Solution (mine, at least): Ensure the restriction for Installing Apps is active, not disabled. Under settings, check General | Restrictions | and ensure Installing Apps is allowed.