Hello Marc,
Surprise, surprise, surprise! In the classic method of solving software issues, I uninstalled everything VSL related, including the Synchron player, and reinstalled it all fresh. All the files got updated to newer versions and now it all works correctly. I can also load and play your Prokoffief file. I suspect that because of numerous Apple software upgrades recently, that my original VSL files became unstable and needed refreshing.
All the best,
Lee
P.S. I still want NP4!!!