Haven't heard of that error before, but I have a suggestion to try. When you setup your Facebook application, you specified a Site URL, let's say 'http://www.domain.com'. In the JFBCInvite module's parameters, make sure that the Inviter Thank You URL and Inivitee Welcome URL are both in that domain, like: http://www.domain.com/thanks and http://www.domain.com/welcome
That error (in other cases at least) generally means that Facebook thinks your trying to send people outside of your application, and they don't like that.
Hope that helps, but if not, let us know!