In March 2011 Automattic replaced their WP Stats plugin by a new one, called Jetpack. I initially couldn’t get that plug-in working. It kept throwing up an error message ‘site_inaccessible – Error Details: The Jetpack server was unable to communicate with your site [HTTP 412].’
The support team of Automattic couldn’t figure out what was going wrong but fortunately my hosting company ICDsoft could. Apparently they block certain access attempts for WordPress sites. They sent me the following explanation and solution less than 20 minutes after I reported the problem:
We have a special set of rules on the server that are employed to prevent most popular hacking attempts. The xmlrpc.php module of WordPress very often is a target of hack attacks, that’s why we have a rule that disables the access to it. Please add the following code to the .htaccess file in the WordPress directory of the account:
After making this modification, Jetpack worked just fine.
I had to reapply this fix in December 2011 after updating the theme of the site. For some reason the .htaccess file had been reset during that update.