Solved! (I think). My friend has just sent me a changed setlist and I noticed that the song titles have changed since the list I was working from! The old song name was, for instance, 'The Gambler Custom Backing Track' he has now shortened it to 'The Gambler' without realising that this would cause problems. So Peter you were right!
We are going to test things out tomorrow now that I have altered my song titles to suit. One good thing that came out of this is that there was a lot tidying up needed in my song book where songs are no longer needed as they were there to try out and not wanted later.
Thank you everyone for your help.