I have been unable to set fiddler as the system proxy ever since updating to the Windows 10 "creators update"(Version 1703, build 15063.332). All fields on the LAN settings window are blank, and it won't let me update them. I enter "127.0.0.1" and "8888" and after the advanced settings window closes, clicking "ok" does NOTHING!!! Reinstalling fiddler ALSO does NOTHING!!!!
After one cumulative update of Windows, the problem got worse:
" 22:17:47:1692 ! WARNING: Port 8888 is already in use (for at least some IP addresses) by 'mobileservice:13340' "
At startup, a dialog asks to reassign fiddler to a different random port. If I decline, the attached error dialog shows up.