Net,
Sorry for the delay in getting back to this. We were travelling this weekend for Joomla Day New York.
For the Overview page, my guess is that your Domain URL isn't set properly. You shouldn't include www in the app-domain setting in the Facebook configuration. If that doesn't seem to be in, can you check to see if the URL you are on is the cause of the error: if you're on
www.xxx.com it may tell you to use just xxx.com, and if you're on xxx.com, it may say
www.xxx.com
Either way, the warning we give there is just a warning. In some configurations, even with the warning, everything can still operate just fine. If you're able to login through Facebook, that means that things are good.
As for the Invite module, there's been a few bugs in that on Facebook's side recently. If you can post (or private message) the URL of the page you're using the Invite module on, we'll gladly test and let you know what we find.
Thanks,
Alex