Two interesting additional facts !
1. I have found that Biab 2007, on the same notebook, and with the same set-up, has similar problems. With both NC and Biab 2007, the problems extend at times to actually locking the application.
BUT
2. I have down-loaded the free Notation Player, and that is perfectly happy
with the set-up - configured itself and plays the file perfectly.
Does this give any clue as to why Composer is 'gibbing' ?
(Obviously I'm somewhat less content, in that Player doesn't have the flexibility of Composer in terms of eg part-display or indeed midi-editability. ie Player isn't really a viable 'solution' for me.)
Ian G