ID4175: The issuer of the security token was not recognized by the IssuerNameRegistry

Q: IIS threw this error and we couldn't track down the problem for days.
ID4175: The issuer of the security token was not recognized by the IssuerNameRegistry. To accept security tokens from this issuer, configure the IssuerNameRegistry to return a valid name for this issuer.

A: A lot of solutions to this problem return in Google searches.  The one that worked for us was to review the contents of the web.config.  When we copied the trustedIssuers section of the web.config into a new text file in Notepad++, we noticed two question marks inside the thumbprint.  We removed them and copy/pasted that back into the web.config and the site started working.

        <trustedIssuers>
          <add thumbprint="??373837278289473732" name="https://adfs-host/adfs/services/trust" />
        </trustedIssuers>