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 which blocks access to ajax functionality required by the web site.
Try this – simply add the following lines to the .htaccess file in /wp-admin above the existing lines starting AuthName
Allow from all
Hope this helps. 🙂