Global Site Search plugin not working on some sites

In some sites it's working fine, for instance:
http://coldplay.buzzr.com/site-search/?phrase=wikipedia

But in others I can't make it work, for instance:
http://fixer-site.buzzr.com/site-search/?phrase=wikipedia

The plugin is updated and I'm on the latest Wordpress version, I tried also disabling and enabling global site search again. do this happen to anyone else?