This may not be specific to Win10, to be honest I've never tried it before. We have an old phone system, the administration of it is through a dumb terminal with RS232C connection. I have replaced the terminal with a computer. I'm using PuTTY connected to COM1 to administer the phone system. Everything works well when I'm connected locally. The reason I did this is so I can administer from somewhere else. My desk in a different part of the same building, or from home over VPN. In either case I will connect to the computer with RDP. Problem is, when I'm connected remotely, I cannot get the COM port to do anything. If I walk back in there and login locally, I get a popup from putty about a serial port error. Then I can restart the session and it will connect. Once I'm connected, I can then go back to my office and connect to the machine over RDP and it works. But if the connection ever drops, I have to login locally again. I am not talking about serial port redirection. The RDP host machine is the one with the serial port. It just doesn't work from a client connection. Did I miss some configuration step somewhere?