Have you gone through the Facebook App Review process yet for the manage_pages permission? If not, that's likely why you're seeing that error. To test, you'll need to set your Application into "Development Mode" in the
Facebook Developer Area
.
Once in development mode, you should be able to authenticate and test the feature. That should pull in the data to populate the stream as well and you may not need to go through the App Review process, but your results may vary.
After you have tested the permission, please make sure to switch back to Live mode so that other users are able to continue authenticating.
I hope that helps, but if you need anything else, please let us know.
Thanks,
Alex