Error message: "The server committed a protocol violation" when attempting to debug ASP.NET

Article ID	1058	Posted Date	11/9/2006
Product(s)		Updated Date	11/9/2006

Problem: When attempting to interactively debug an ASP.NET application in Visual Studio 2005, the debugger fails to launch and returns the message "Unable to start debugging on the web server. The server committed a protocol violation. Section=ResponseStatusLine"

Background: This error usually occurs when you have set up Visual Studio to debug an existing web application running in Internet Information Server (IIS) rather than the built in ASP.NET debug web server. IIS by default listens for web requests on port 80. In this case, another application is already listening for requests on port 80. Typically, the offending application is Skype, which by default takes over listening on ports 80 and 443 when installed.

Resolution: In Skype, navigate to Tools -> Options then select the Connection icon in the left hand pane. De-select the option "Use ports 80 and 443 as alternatives for incoming connections." You must restart Skype for this change to take affect.