Thank you Jim and Videotrack.

I have nothing complicated. I am using 2019 64 bit with the settings I have always used in previous versions together with Coyote WT or Cakewalk TTS-1. I have no external equipment, midi or otherwise. Output is through the PC's sound card.

Taking Videotrack's advice I have installed some ASIO drivers which as expected have significantly reduced the "driver latency" and also removed the irritating lag when entering melody notes. The error message on starting when using WAS has also been eliminated.

So I now have a perfectly satisfactory system.

Why MME and WAS gave problems I don't know. I guess it's now a case of out of sight out of mind.

Thanks again for taking the trouble.