Many Thanks Both,

Mac: you're right - as ever.

The VSTi looked to be loaded as normal, but in fact, something wierd had happened with the file and there was another synth in there (as well?) somehow.

I now have a new Rule #1: "When something very wierd happens, assume its a corrupted file, and re-do it, rather than wasting ages trying to sort it out."

All Thanks again. Best - Andy