HDCP Message When Trying to Mirror

I tried once before with a similar query regarding trying to watch my movies from my laptop to a tv but only got a response that said I need to adjust Firewall settings. Well I have followed that advice and am really no further forward.

I can view movies directly from I-Tunes on my TV - which is a Sharp Aquos HD job.

My laptop is a 2017 MacBookPro Retina running High Sierra.

My Apple box is connected to the TV via a HDMI cable. Apple Model A1469 - approx 3 years old.

I updated my Apple TV box last week when I first had problems.

I can call up a movie from my purchased items and get presented with the movie cover.

As soon as I press play my laptop screen and oviously my tv screen show a greyed display. On top of the greyed display I get a message that this movie can only be played on a HDCP display. Try switching your I-Tunes to a separate display.

This happens whether I select a HD movie or a non-HD movie.

So what is going on with this set-up.

I-Tunes displays ok directly, I can mirror my laptop displays ok, but as soon as I try to play a movie from my laptop it all goes to ****.