Thank for the information on Rebuilding the list. That did the track although I'm not entirely sure why. To rebuild the list I had to select the current style in order to get access to the Rebuild button. The list did contain a large number of styles. Anyway, it did the trick and it worked as I had assumed it would from previous work.

With regard to midi track generation. I selected a region of a midi track and then Generate Midi and selected Guitar from the list. No style list was provided but I got a message that Guitar was not available in the current style. That was correct of course because the current style was RealTeracks. I thought that I could select a midi style in the same way I chose a RealStyle! If I select a new style with a Guitar part in it then this will work, but I don't want to select a change of style for the song.
But I guess the clue to what I'm doing is that there is not an option to Select and Generate Midi. I am obviously misunderstanding something here.