When I return a StatusDescription with a newline using the HttpStatusCodeResult from ASP.Net MVC 3.0, the connection to my client is forcibly closed. App is hosted in IIS 7.
You can't have a linebreak in the middle of an HTTP header.
The HTTP protocol specifies the end of a header is a line break.
Since the line break is in the middle of a header, the header is not a valid header and you are getting this error.
Fix: Don't put a line break in the middle of an HTTP header.