Summary:

A login prompt may appear when logging into CRM using IIS autologin. On entering a username and password, a 401.5 (Unauthorized) error page may appear.

Resolution:

This issue may be caused by having Anonymous authentication enabled on the CRM virtual directory in IIS. When using IIS autologin, only Windows authentication should be enabled.

More information:

The following may assist in troubleshooting IIS autologin cases:

  1. On the client machine, open a command prompt and run the "whoami" command. This will return the domain\username you should be using in CRM. The domain goes in the Default Domain for IIS login field in Administration -> Users -> User Configuration. The username should match a user logon in CRM.
  2. Enabling the full CRM sql logs may be useful, as the username being used by CRM will appear in the logs.
  3. IIS Failed Request tracing can be used to identify the source of HTTP error codes (401, 404, 403 etc) returned from IIS.
    More information is available here: http://support.microsoft.com/kb/942078