An error message is information displayed when an unexpected situation pops up. On modern graphical interfaces such as computers and what not they happen a lot, for a lot of reasons, the most famous of them being the blue screen of death. There are many other not so popular ones though. You have access denied, low disk space, out of memory. Stuff like that.
As of yet there is no error message for internet censorship, but given how things are going, there will be a mighty need for one soon. Error 451 should be a thing.
The Protoculture Mixtape v.92 Issue : Games : Registry