For several friends I've shown them how to use their laptop to connect to a ROKU TV or a ROKU adapter.  All have Windows 10 and it's simple, press the Windows key and the letter a.  Then in the activity center on the lower right click on connect and when the ROKU device shows up, click connect.  Click allow or always allow on the ROKU device and from that point on your computer casts to the TV.

Never had a problem until yesterday.  A friend just returned from vacation and had pictures on his computer we wanted to see on the big screen TV.  He was using our WiFI with no problem and our ROKU device showed up as expected.  When he tried to connect it asked the usual, allow, always allow etc. and we said always allow but each time it would fail to connect.  His is a 6 month old high priced Windows 10 computer and he has nothing on it except software to run a CNC machine.  I looked at the network connections and blue tooth etc. and saw nothing odd.

Any suggestions why there's no problem with my Windows 10 laptop connecting but there was with his.  There's no security on our WiFi as we're too far from anybody to be concerned about an intrusion of theft of service.  He had no problem using our network for browsing.