I‘m using Fiddler2 (or trying) to capture SSL traffic for a windows desktop gadget hitting an https web service. It used to work, and then it stopped a couple days ago, always with this error:
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Unable to Generate
Certificate
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Creation of the interception certificate failed.
makecert.exe returned -1.
Results from C:\Program Files\Fiddler2\MakeCert.exe -ss my -n
"CN=DO_NOT_TRUST_FiddlerRoot, O=DO_NOT_TRUST, OU=Created by
http://www.fiddler2.com" -eku 1.3.6.1.5.5.7.3.1 -r -cy authority -a
sha1
Error: Can‘t create the key of the subject (‘JoeSoft‘)
Failed
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To configure Fiddler to capture web traffic from window, just follow these steps.
1.open Fiddler. Click Tools, Fiddler Options..
2.Select the Connections tab. Fiddler listens on port 88888 by default but can be changed here if needed. Make sure the ‘Allow remote computers to connect’ option is checked. It is not checked by default.
3.Click OK. You will need to close and re-open Fiddler for the changes to take effect.
4.Once Fiddler is re-opened, make sure it is capturing traffic by clicking on File. The Capture Traffic option should have a checkmark next to it. 
[Fiddler]Unable to Generate Certificate
原文：http://www.cnblogs.com/jacksundatashare/p/4981640.html