Happened same with me. This is happening because the App Store is looking for a working connection on en0 port and it is not getting anything anything on it due to which it says the device cannot be verified.
Your task is to switch the en0 and en1 assignments basically.
Just copy the files 'preferences.plist' and 'NetworkInterfaces.plist' from
/Library/Preferences/SystemConfigurationto Desktop as a backup and delete it from/Library/Preferences/SystemConfigurationRestart your Mac and try to login into the App Store
Worked for me!