What to do if you receive the following error during Jetpack installation:
Your website needs to be publicly accessible to use Jetpack: site_inaccessible
Error Details: The Jetpack server was unable to communicate with your site [HTTP 403]. Ask your web host if they allow connections from WordPress.com. If you need further assistance, contact Jetpack Support: http://jetpack.me/support/
In order to activate Jetpack you need xmlrpc.php file. First add the following rule to the .htaccess file:
<Files xmlrpc.php>
Allow from all
</Files>
After adding the rule also deactivate Pingback possibility in WordPress http://en.support.wordpress.com/comments/pingbacks/