fiddler2 unable to generate certificate

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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(I swiped the error from the google group for fiddler, although I just posted my own and it should be visible soon).

Has anyone else had this problem and solved it? Is Fiddler just broken?