A DigitalPoint Forum thread has details on a new tool available to a select few Google AdSense publishers. The new tool is named "Site Diagnostic" and reportedly does the following;
This feature provides diagnostic reporting on errors our crawler encounters when attempting to serve ads to your site.
We've detected that you may have certain sites that our crawler is unable to access, so we can't deliver relevant ads. Using the Site Diagnostic feature, you can review the reasons why we weren't able to crawl a page and resolve the errors in order to receive more relevant ads.
If you want to see a screen shot, you can visit the thread or click here.
Forum discussion at DigitalPoint Forum.