I ought to add that PlexMediaServer is running fine and I can access it in my web browser. On the Apple TV the trailers app is correctly hijacked and I see the Library, Channels and Settings menu, and settings works perfectly showing that it detects the PlexMediaServer.
It's OK. Managed to sort it by finding a backup of my original PlexConnect folder. I copied all the files over and it started working. Have now set it up as a service and all is well. I don't know why the latest version of PlexConnect didn't work. Have there been any changes to how things should be set up?