Recently experienced a 418 Unused Error on one of my WordPress websites.
unused The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, email@example.com and inform them of the time the error occurred, and anything you might have done that may have caused the error. More information about this error may be available in the server error log.
I tried clearing cache and cookies as suggested in this WordPress Support thread, but it somehow did not work for me. Changing the password for the user in the database I was trying to log in with did the trick in the end.
NB Sometimes it can also be due to too many failed login attempts. See Dreamhost Forum Thread here.
Featured Image Columbia unused stamp ca 1859