If you have protected your WordPress Admin folder (eg /wp-admin) using .htaccess authentication, you may find that your site design breaks or some features don’t work.
This can be due to Ajax functionality failing because of the .htaccess authentication is blocking access to the Ajax functionality required by the web site.
Try this – simply add the following lines to top of the the .htaccess file in /wp-admin
Allow from all
Hope this helps. 🙂