I have a .NET 1.1 solution where all projects have been upgraded to .NET 4.0 (VS2010, Windows 7). To get past my "Unable to start debugging on the web server" problem, I switched my web application property to use VS Development Server instead of IIS.
When debugging the web application, it launches OK. But I get the above error when I hit a line where I call a web service that's local on my machine. I've seen stuff about adding useUnsafeHeaderParsing=false, but my web.config doesn't have a sytem.net section.
Is it not able to server the web service as well as the web application simultaneously on the application development server? Do I need to get it configured correctly to use IIS7? As a longtime IIS6 user, just looking at it makes my head spin... although, I do have the site and webservices set up within it, and I am fairly certain it worked at one time. Gotta love that.