biswebteam Hi. I understand, but I've just tried to configure it on my copy of Feed plugin and haven't got that message, so I still suspect something is missing in configuration. Anyway to exclude a possibility of a broken/corrupted file or having old version of plugin please reinstall plugin and see if it makes a difference.
I'm afraid next step would be for me to look into Your Facebook settings, so we would need to schedule a Skype session (my login on Skype is "teitbite") so I would be able to look it up during screen share.