Different geographical locations. Thus connecting over the Internet.
Windows 10 at home, Windows 7(1) in an office and Windows 7(2) in another office.
Yes. Ports and IP are identical – using the ones given by NoMachine in its connection window.
That is infact why this is so mysterious. Identical settings on all fronts, yet from Windows 7(2) no matter what it errors 138.
PS: Unfortunately I see my uploads are being blocked here in the forums, how should I upload them to successully deliver them?