Best answer by Stanley_4
Now that you have done that factory reset he has lost everything he had on his unit and you need to start over from scratch once you find and fix the network problem. The first thng I would check is the guest network and see if "client isolation" or a similar setting is turned on, that will prevent different units hooked to the guest network from communicating.
Once you have that sorted you'll need to go back and do a new system setup, probably easier if you can wire the friends unit to the guest network. You do not want to add it to your system but create a new second one. The FAQ has instructions if you don't have your original ones handy.