Yubico/yubiauth — pull request #4 by jhofmann (2014-06-25 16:28:57+00:00)
Title: Fixed a bug where unassigning a YubiKey would cause a server error

If you tried to unassign a YubiKey (that could or could not exist) from an
existing user to which this YubiKey was not assigned, the server would
reply with "A server error occurred. Please contact the administrator."
and log a stack trace.