Scheduling Posts & Trackbacks Error

I always get this message when I post: “One or more errors occurred when sending update pings or TrackBacks. Check the Activity Log for the error.” What does this mean?

The schedule function has never worked. (i.e. I can’t schedule posts to automatically be published on a certain day and time). When I schedule a post to be published on a certain day and time, it does not become published. How can this be fixed?