What causes this error when logging into Active Directory in a system that was working:

There is a technical set of reasons around the AD request and rules as to why this 'has' to be reported as an 'Unexpected Error'.

This can be caused by:

• Changing the server (replacing an old server with a new one, but the configuration still points to the old one)
• Changing the service user account that LoginHub uses to login to AD with

  There are a few additional edge cases and maybe some unknown ones, but those are the overwhelming causes. The other edge cases need to be located in the log file to be diagnosed.

You need to restart the LoginHub application pool after changing those settings.