If you have looked in your site diagnostics tab in your AdSense control panel lately, you will see a bug that displays a robots.txt error, meaning you are disallowing the Google AdSense mediapartners bot from crawling your site. The only problem is that it is displaying errors based on the Google cache URL, instead of one of the publisher’s URLs.
I spoke with Google, and this error is being fixed. However, it does not affect ad serving, if someone views your site in Google cache, they will still see ads which are credited to the publisher with their intact publisher IDs still in the code. It just makes it hard to find any other issues in the site diagnostics tab, especially if you have a site with a lot of cached page views.
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