HTTP request status error
Drupal cannot contact itself. The system module reports this error when a system_check_http_request(). Assuming this is the cause of the AJAX errors, you could try, as the error message suggests, to set $conf['drupal_http_request_fails'] = FALSE; in your settings.php file. This might fix the symptoms, but not the cause however. 

The fix lies in figuring out why this check fails:

drupal_http_request(url('', array('absolute' =&gt; TRUE)), array('max_redirects' =&gt; 0));


It could be that url() is not returning your front page URL. If you have drush on your server, you can run the command drush php-script my_test_script.php. With my_test_script.php containing a simple test script: 

&lt;?php echo url('', array('absolute' =&gt; TRUE)), array('max_redirects' =&gt; 0); ?&gt;


If it is returning the correct home page URL, another likely problem, since you're hosting multiple sites, is that your domain is not resolving the correct virtual host. You can test this with the server command:

wget -O- http://www.example.com/


If your site's home page HTML is output to the console that should tell you that the server can contact the resolve &amp; connect to itself. If this is the case it might be something like a PHP config preventing retrieval of HTTP URL's.