Apologies for not replying sooner. Well I did, but my reply seems to have disappeared. The gist was that I have tried the various approaches to key focus, including there being none at all when there is just the main window open. As to the command i am trying to use, that doesn't really come into it because the error messages start up before I have done anything except switch on.
The breaking news though is that the problem has fixed itself. Logic remote on the ipad AND the iphone are working fine, so the problem, whatever it was, seems to have been with Logic pro itself, but I can't imagine what I had switched on, or off, that I shouldn't have. All part of the wacky digital world.