There was an error in the App Store. Please try again later. (100)

I can use my iPad, iPhone with this account to buy applications. But I can't use my iMac to buy any apps, even the free apps. It always appear "There was an error in the App Store. Please try again later. (100)"

I used to use my iMac in China and applied the account when I was in China. Now I am in U.S., is there anything related to this?

What can I do?