I am getting the same problem as this:
http://stackoverflow.com/questions/425016/debugging-w-attach-to-process-starts-asp-net-dev-server
Every time I attach to the web server, I get another asp.net development server, eventually ending up with more and more.
However I don't see the option described in my Properties page. I have Visual Studio 2010. All I have in the Properties is "Full Path" and "Opened URL".
EDIT: Note: they all have different port numbers