This dreaded message is typically caused by an improper connection to Facebook. If you haven't connected your account to Facebook, follow the instructions of the following video to do so.

Connecting to Facebook

If you have connected to Facebook and are getting the Error message, you'll want to disconnect your account from your Facebook profile and then reconnect it. Afterward, be sure to do a Hard Refresh on any of the articles you attempted to share. You can do this on windows based web browsers by holding CTRL and hitting F5, or on Macintosh Safari by holding Shift and hitting the Refresh button.

This should get everything posting correctly again.