Problem

I get a System.NET.WebException "The underlying connection was closed" when calling into WebServices.

Solution

When debugging a .Net application through Fiddler, you may see a System.Net.WebException, with message "The underlying connection was closed: A connection that was expected to be kept alive was closed by the server."

This is a bug in your application (it should handle this type of exception).

This problem is very unlikely in Fiddler Classic 2.2.8.5 and later, due to enhanced client connection reuse support.