set static IP, gateway and use Google's DNS 8.8.8.8 and 8.8.4.4, reboot your router, reboot your 3DS, run NTR, press X & Y and run debugger, turn off Windows firewall temporarily then run as admin the Window debugger, it shoud work that way
I had same issue on 2 N3DS with two different routers until I did that.
I had same issue on 2 N3DS with two different routers until I did that.