Debugging VS2008 ASPNET Apps Under Vista

I've run into a bizarre problem that the Microsoft guy over on the vsnet.general forum said I should raise here because it looks
like it's a Vista-related issue.

I have Vista Ultimate installed on a desktop and a laptop. I use Visual Studio 2008 on each machine to develop, among other things,
ASP.NET websites. I use the internal development webserver in VS2008 (i.e., WebDev.WebServer), rather than IIS, as the hosting
environment.

Yesterday VS2008 on the desktop stopped being able to debug websites. Suddenly, IE7 refused to display the webpage being debugged
(this happened in the middle of a build/debug cycle; I hadn't added any new hardware or software). VS2005 was also unable to debug
websites. In addition, "attaching" WebDev.WebServer to a very simple site (i.e., just a single index.html file containing a simple
text string) didn't work either. The error message was always "Internet Explorer cannot display the webpage".

I also ran into problems when trying to use Firefox to access the test sites.

When VS debugs ASP.NET websites it addresses them in IE as http://localhost:<some port number>/<web page>. Walter (over on the
vsnet.general forum) suggested that I try substituting 127.0.0.1 for localhost. This fixed the problem, although it wasn't a
solution because I don't know of any way to configure VS to use an explicit loopback address rather than localhost.

But it got me thinking about a time when my hosts file was hijacked. In checking the hosts file I saw that it contained only two
lines (other than comments):

127.0.0.1 localhost
::1 localhost

Not being familiar with IPv6 loopback interfaces at the time, that second entry looked weird to me, so I commented it out.

Which then solved my problem; localhost mapped to 127.0.0.1, VS was able to debug and I was a happy camper again.

But I'm still concerned about >>why<< commenting out that line solved the problem, and why the problem occurred in the first place
(since both those entries are apparently part of the default hosts file on a Vista system). I've never done anything to the IPv6
configuration that was created when I installed Vista (as I mentioned, I know almost nothing about IPv6). So I've got a situation in
which some networking component "failed" (or at least changed) unexpectedly.

Why would a working resolver environment suddenly go bonkers?

- Mark

p.s. I just remember that I tend to install all recommended updates. On 1/12 I installed both a new Windows Defender definition file
(1.24.5399.0) and an update to the Marvell Yukon PCI-E Gigabit Ethernet Controller which was released back in December 2007. Is it
possible that one or both of these updates caused the problem I'm experiencing? I was successfully debugging sites after installing
both packages, which argues against them being involved.