Cannot login to iCloud, App Store and iTunes Store after installing EI Capitan
MacBook Pro 15" Retina, bought in early September. Everything was fine and migration from my old MacBook Pro was smooth. Then on 3 Oct, I downloaded the new EI Capitan and installed. After installing EI Capitan, I was asked to sign in to iCloud. After I gave correct Apple ID and password, a small box titled "Verification failed" appeared with the message "This action couldn't be completed. Try again." The same message appeared when I tried to sign in to App Store and iTunes Store.
I have contacted Apple Telephone support five times and talked to a few products specialists. It seems everything is fine, and last night one technician asked me to reinstall EI Capitan. And I did. Unfortunately, the same problem and message remain.
Any suggestion? Thank you in advance.
MacBook Pro (Retina, 15-inch, Mid 2015), OS X El Capitan (10.11), Sign in to iCloud, App Store, iTune