The feature to Block XMLRPC Access uses an entry in your .htaccess files to prevent Apache from accessing the WordPress XMLRPC URL. If you are usign nginx or some other web-server (other than Apache) then this .htaccess restriction will have no effect.
If you are using Apache but my plugin cannot detect it for some reason (maybe you have limited the information your server provides about what software you are running) then it should still work for you. You can still click on the “Block XMLRPC Access” button even if you see that warning but it just may not have the desired effect unless you really are using Apache 
