Hello and welcome to JustAnswer! I am Pete, a TV expert, and I'm happy to assist with your question today.
Have you restarted both your modem/router and the TV?
Turn both off, then power on the modem/router first, give it a few minutes to get up and running, and then turn on the TV and see if you still have the handshake error message.
This error is usually caused by a router problem, and restarting your router should solve it.
If you are still have problems, just let me know.
Do you need any further assistance with this question?