To improve the ability of Webmasters to identify and fix crawl errors that are associated with erroneous redirects, Google Webmaster Tools has changed the manner in which these errors are reported.
In the past Webmaster tools would generate an error report on the directing URL. They have changed this to report an error on the URL that is being directed to.
When URL A has a redirect to URL B and URL B is non-existent an error will now be reported on URL B rather than URL A.
This change simplifies the diagnosis of crawl errors by Webmasters. You can use your tool of choice, such as cURL, to check that this error is really occurring and to rectify it.
These reporting changes can also change the total error count that is reported for your site, particularly if you are redirecting from one domain to another, since the error will be reported on the domain you are redirecting to, rather than the domain of origin.
This change will only affect the reporting of these types of crawl errors in Webmaster Tools. It will have no effect upon a site’s ranking or indexing.