Just one more thing I've discovered which may help others, or maybe I should have been aware of this?

I couldn't open any songs from an external HD, originally used on Windows but I downloaded software to be able to use it on my Mac (Tuxera disc manager) they will open from a USB stick, at least the couple of songs I've tried to open, and will open if they are moved to the laptop or computer. It really is a process of elimination by the looks of things.

I have a Mac external HD that I will drop all BiaB songs onto and see if that works or not.

Hopefully this may save others some time and frustration or maybe it's just compatibility issues between operating systems and no-one else swaps from one to the other as I do, either way, for what it's worth I seem to be making headway and slowly solving the original problem.

Andy