I've been running Amazon Machine Tags on my site for over a year now, and in the last couple of weeks I've noticed that it's stopped finding the correct Amazon store based on IP location.
According to the wp-content/cache folder, it stopped working on 27 March (ie that's when I last had a non-US request cached). Since then it's just been returning prices from the amazon.com store, the default in my Amtap settings. I've no idea why things may have changed on 27 March - I might have been doing some basic site maintenance but nothing major.
I've tried disabling all plugins apart from Amazon Machine Tags and IP 2 Country, but no luck. I have the amtap-aws-key-verification.txt file set to 'true'. Is there anything else I can do to get this working?