Fiddler doesn't capture HTTPWebRequest

问题:

I am new to Fiddler, pls help. my IE is capturing HTTP request of Client Webform. However it will send HTTPWebRequest (POST) on click event of Button control. I am unable to capture this HTTPWebRequest in Fiddler. Fiddlers default listen port set to 8888, so I have update my web.config as well, as shown below.

<system.net>
<defaultProxy>
  <proxy usesystemdefault="True" proxyaddress="http://127.0.0.1:8888"/>
</defaultProxy>