Ipad2, unable to purchase/update existing Apps

extremely frustrated. I am in Australia, and have Australian address and email address in the Apple system. I have my account in good credit. My problem,( only just started,) - when I try to install a new App, or when I am trying to update and existing app I get the response "Account not in this store. Your account is not valid in the US store. You must switch to the Australian store before purchasing"

I have never had any problems, and nothing has changed. I am now stuck with apps that I cannot update. My ipad is using ios6.1.3 (the most recent)

Can someone give me some guidance. Many thanks ironsheikh51

I have not posted to community boards before, so excuse me if not politically correct, thanks