Is your ethernet connection set at "en0" ?
I fixed this issue in a thread I started a few days ago:
"For those of you who can't login to Appstore, make sure your Ethernet built'in is set à en0 (you can see that in System Information, ioreg and Network utility). If not, then go to Network in System Preferences and delete all your devices, apply, then deleteLibrary/Preferences/SystemConfiguration/NetworkInterfaces.plist. Reboot, go to Network in System Preferences again and add your Ethernet connection FIRST. You're good to go!"