Cant login with apple id and pass. Cant download anything from App Store !

Question

Hi when i try to download app from App Store it shows me login screen I fill all of them as true, but it says "Unknown Error. " and "There was an error in the App Store. Please try again later. (4)  "     I can't install any app. Help me

Answer 1

1. In the lower right corner of the App Store window is a round button with the image of a flag. Clicking that button takes you to a page where you can choose your country by flag. You may have to scroll to the bottom of the window to see the button. The country must match your billing address on record.
2. Back up all data before proceeding.
Triple-click anywhere in the line below on this page to select it:
/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist
Right-click or control-click the line and select
          Services ▹ Reveal in Finder (or just Reveal)
from the contextual menu.* A folder should open with an item selected. Move the selected item to the Trash. You may be prompted for your administrator login password. Restart the computer and test. If there's no change, restore the item you deleted from a backup, overwriting the one that may have been created in its place. Otherwise, you may need to recreate some of your settings in the Network preference pane.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select
          Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.
Credit for this solution to ASC member luis.pinho.