Fiddler 4 Certificate error on Windows

Well, it seems that in the end it was a Windows Issue. My PC is part of the company Domain and even though my user was an Administrator of this PC, not everything was fully functional (for example I could run as Administrator any app with no problem, but couldn't create a Root Certificate). The issue was found by my colleague in the Windows Credentials Manager and he fixed it with the following Registration Entry (.reg):

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\Protect\Providers\df9d8cd0-1501-11d1-8c7a-00c04fc297eb]
"ProtectionPolicy"=dword:00000001

I hope this helps someone avoid hours of searching on the internet for a fix.

You need to reset Fiddler Root Certificate , After that everything will be fine