LMS not playing tracks anymore

I've LMS v7.7.2 installed on a Vortexbox, and until recently all was OK. I've not made any changes in settings etc.
Now however I can't play any tracks.
At the moment I am on my Imac which is cabled to the Vortexbox and I'm using LMS through the Vortexbox GUI.
I can load all my music files, and select them (at least on the lhs of the GUI screen), but they do not usually appear on the rhs (occasionally do), and certainly don't play.
I assume I am 'Player 1' in this situation (certainly not the SB3, Touch and raspberry Pi / Picoreplayer I have elsewhere in the house).
Player 1 tells me it is using something called 'Softsqueeze'.

By the way, how do I upgrade the LMS version ? I understood all I had to do was hit the upgrade button on the Vortexbox GUI but that has no effect.

Thanks