Can’t buy apps through a USB Wi-FI adapter

The Wi-Fi card in my girlfriend’s 2011 MacBook Air failed, so she’s using a USB Wi-Fi adapter, which works fine. However, she cannot sign into the App Store or FaceTime. An error says "your device or computer could not be verified. Contact support for assistance". Bryan McGill The App Store, iCloud, FaceTime and several other services use the MAC address of your computer as part of the verification process. This doesn’t refer to Apple Macintosh; it stands for Media Access Control and it is a unique serial number hard-coded into every network device by its manufacturer. Your IP address will change between sessions and locations, but a network interface’s MAC address will never change. The USB adapter is a network device in its own right, with its own MAC address. When you access the App Store through it, you are using its MAC address, not the one that was originally authorised for the built-in Wi-Fi adapter. This trips an intruder alarm at the App Store and it locks you out. You should be able to fix this quite simply. Delete /Library/Preferences/System Configuration/NetworkInterfaces.plist, then log out and then back in again.