If you try to trace your web applications using Fiddler with default settings under Windows 7, you will get the following error in your browser:
[Fiddler] Connection to localhost. failed. Exception Text: No connection could be made because the target machine actively refused it ::1:80
This can be fixed by disabling IPv6 in Fiddler:
1. Go to Fiddler, then Tools > Fiddler Options. 2. Uncheck "Enable IPv6 (if available)".
Tracing should now work.