You'd usually only get that error if you are trying to set a cookie or do something with the session after you've already echoed something, or otherwise sent something to the browser. If you're using an unmodified Community Auth examples controller, I don't have any idea why you're having the problem you are having, but it would require that you do some debugging. I'd say that you should for sure take a close look at the Community Auth documentation regarding installation and make sure you did each step. That way you can be sure you're not having a problem with Community Auth. Community Auth is well tested in the wild, and if something was wrong with it, there would be a bunch of people leaving similar comments here in the forum. Beyond that, I can possibly help you figure out what's wrong, but I'd need access to your server. Another option would be to zip up your site with a database backup and make it available for me to download.
