So, here's the situation, and any help is greatly appreciated, I've banged my head on the keyboard for hours trying to figure this out. I've searched forums, searched Microsoft's Support site, and must be blind because I can not find a solution to my problem. I have a client, who has a website that I provide hosting for, using IIS 5.1 on a Windows 2000 Server environment. Now, any user accessing the site must provide login credentials before they even get access to the website. My client previously had all hosts running Windows XP, and had no issues logging in. They recently upgraded to Windows 7, and now, when anyone using Windows 7 tries to login to the website, they receive the prompt to login again, and eventually, after 3 tries, the HTTP 401.1 error. I've researched and realized the issue may be with loopback check procedure, and disabling it, or possibly something to do with anonymous user authentication default Windows 7 settings. Any help with this issue would be GREATLY appreciated. Thank you in advance!