Perplexed with audio not playing

Hi,

I've been using FTR for many years now and never had a problem.  I've just got some recordings to transcribe.  They all load and appear to be playing okay, but no actual audio comes through.  The only difference I can see between these tracks and the many others I have had are that these all start with [FTR0439] whereas others just have the court name and no square brackets.  Any idea?

Thanks