Why does my Microsoft Virtual Server 2005 Administration Web site make me authenticate even though I'm logged on the local network as a user with permissions?

http://www.windowsitpro.com/article/permissions/why-does-my-microsoft-virtual-server-2005-administration-web-site-make-me-authenticate-even-though-i-m-logged-on-the-local-network-as-a-user-with-permissions-.aspx

Why does my Microsoft Virtual Server 2005 Administration Web site make me authenticate even though I'm logged on the local network as a user with permissions?