I installed this plugin in some sites, but there is some kind of bug in one of these.
In this site: liosite.com
Wordpress is installed in a different folder: /system/
I this case, plugin doesn't work: "This site does not have the WP Remote WordPress Plugin installed."
Plugin is installed with correct api key, but i think that there is a problem when site url is different from install path of wordpress. (wordpress works on liosite.com but files are in /system/)