ohh ok. Generation probably did not freeze but if you don't have a gpu it will take like forever to generate (5 minutes probably for large model), which is longer than the duration of the demo. after 3 minutes the demo will close out. if you still want to still try the demo i would recommend going with a smaller model like the medium or small model.
That is a bit strange though for the fluidsynth error... Are you able to hear the notes when you play?