Basic authentication in IIS MVC 3 site not working

I have just deployed an MVC 3 site to my Windows 2008 Web Edition (IIS 7) server, and am trying to set up Basic Authentication so that it will not allow unauthorized access. This seemed to work at first, but once I was troubleshooting a problem and making changes, now that this issue is fixed, my basic authentication for some reason no longer works -- it's letting anybody on.

Under my Authentication settings in IIS7, I have Basic Authentication enabled, and all other forms of authentication disabled. I've also tried other various combinations, and so far, everything I've tried is leaving the site wide open.

I wondered if it was caching my credentials, so I tried from a different browser from which the site has not been accessed, and it's still leaving it open.

Am I overlooking something obvious here? I thought all I had to do was leave all forms of authentication disabled, except for Basic? Any ideas what could be going on?

If not, any ideas on what I could do to troubleshoot? Is there anything I could see in Firebug to see what may be going on?

Thanks in advance.

Ultimately, this was what I was trying to accomplish, I just wasn't sure how to articulate it. After reading the article linked in that answer, I'm going to try to figure out a different way to limit access to this site (either by IP or using my single-level authentication).