last updated Jun 23rd, 2014 8:14 CEST
This site and most probably many others are experiencing problems with the Yahoo Site Explorer service. More specifically it is the Google (XML) Sitemaps Generator for WordPress plugin being unable to notify Yahoo about the changes in the sitemap structure.
The explanation is simple - Yahoo has discontinued their service. It has been moved over to Bing so the way to setup your plugin is: enable Bing and disable Yahoo notifications. Complicated code changes or workarounds you can find in older blogs will not work.