That occurs when the "Invitee Thank You URL" configured in the module is set to a location that isn't on your site. Make sure that if you're invite module is on
www.domain.com, that the URLs in the parameters are set to go to a location on
www.domain.com. Facebook does this as a check to ensure that after inviting friends, you don't redirect the user to a malicious site.
Hope that makes sense. If you continue to have issues, let us know the page your Invite module is configured on, and we can investigate it further from there.