401.1: Access is denied due to invalid credentials.
401.2: Access is denied due to server configuration favoring an alternate authentication method.
401.3: Access is denied due to an ACL set on the requested resource.
401.4: Authorization failed by a filter installed on the Web server.
401.5: Authorization failed by an ISAPI/CGI application.
401.7: Access denied by URL authorization policy on the Web server.