Then...  In Visual Studio 2008 I was trying to run an ASP.NET app in debug mode using IIS.
After a successful compile I got this error message.
Unable to start debugging on the web server. The server committed a protocol violation. Section=ResponseStatusLine.

What does that mean?

Well it means I had Skype running and it was using port 80 and 443.  I needed to change the default skype settings.
Open Skype and under Tools/Options/Advanced/Connection uncheck (Use port 80 and 443 as alternatives for incoming connections).

Hope this saves someone some time.