I recently had a problem getting Fiddler to show the traffic to and from an application running on localhost when viewing the application with Internet Explorer. I completely forgot the workaround so thought a post on the subject would help.
There are some known issues with Fiddler and this is one of them. In short, both Internet Explorer and the .Net framework are setup not to send requests for localhost through a proxy. Of course Fiddler is a proxy and therefore will not receive the traffic.
One workaround is to use your machine name instead of localhost. So, http://localhost:8081/mytestpage.aspx becomes http://mymachinename:8081/mytestpage.aspx.
Another is to insert a dot (.) immediately after localhost. So, http://localhost:8081/mytestpage.aspx becomes http://localhost.:8081/mytestpage.aspx.
See also
The Fiddler website - http://www.fiddler2.com/fiddler2/