This problem had been plaguing me all week.  Every time that I'd try to connect to the admin site for my Virtual Server 2005 box, I'd get an http 500 error and Virtual Server would hang.  If I tried to shut down the Virtual Server service through the Services applet or via "net stop" it would just spin and spin and spin.  The only solution was to kill the Virtual Server process.  Conveniently enough, nothing would show up in the event log to help diagnose the problem other than a warning that the service stopped unexpectedly.  (Really? You don't say? -- Of course it did! I'd just killed it myself!  DUH!)

After much gnashing of teeth, I found a solution in Spanish and thanks to Google's "translate" functionality, I was able to actually read it.  Here's the post.  Here's the machine translated quote that helped:

And it had not tested and works when this problem occurs. Obviously the common VMRC does not work either.

The solution by which I will choose to change the Virtual Server by one who does not have SP1 installed. I think it is too serious a mistake that a VM is that it saves the state can not be lifted again and also not be able to access the site administration.

Sure.  It's not the best translation ever but it got me wondering if there was saved state.  So I took another suggestion from that same forum thread to download the VMRCPlus client and connect to Virtual Server without the admin site (via COM?).

Turns out there was a guest OS with saved state.  I dumped the state and now the Virtual Server Admin Site comes up without problems.

My guess on how this happened is that Windows Update applied a patch on the host machine and then rebooted the server.  When the host server came back up, something was dreadfully wrong with the saved state for that guest machine and it horked Virtual Server.

-Ben