I saw this once before, this may not be recommended from a security point of view in a production environment, but in your web.configweb.config
located at <Web8.5HoneDir>\web\WebUI\WebRoot<Web 8.5 Home Dir>\web\WebUI\WebRoot
add under <system.web><trust level="Full" />
under <system.web>
and all the 401 erors will go away and your Web8Web 8.5 CMS will load up. I think the issue is some permissions youyou may have missed.