Recently, I posted a message about a bug caused by IIS in the browser. I would like to give more precised details.
This happens on IIS 5 under Win2k. It happens on several servers we have this type of install. It causes a bug on IE 6 as well. As soon as you authenticate on the HTTP server, after a while, the IE browser will not able to respond to a post. This will either return a page not found or similar. Closing the browser will do ok as long as you don't authenticate back against the HTTP server.
We had the same reaction on several servers. They all have Win2k with IIS 5 installed.