This is irritating either because SI is finicky or I am stupid. 
 
I have an SI string track that was working once.  I froze the track while working on other tracks. When listening to the project I could hear everything fine.
 
I went back and unfroze the track so I could change some sound parameters(tone).  Now I get no sound.  
 
My ins and outs are exactly the same as some other SI instruments tracks and they have sound.
 
One peculiar thing is I can go into the synth property and change the program and I get sound driven by my controller and also by clicking on the keyboard keys in the synth property.  But when I go back to play the track soloing it or otherwise I get no sound again, controller driven or keyboard key in the synth property.
 
Am I missing something? 
 
I haven't deleted the synth and inserted a new one yet because I'm stubborn and would really like to know why this is happening.  I've had this happen before.
 
 

In case anyone is interested it turns out I am an idiot.  I discovered midi events belonging to another track hidden underneath my string track.  That must have been confusing the synth.  Anyway I deleted unrelated midi events.  Disconnected the synth and reconnected it and everything is fine.
 
I might get this project done if I'll get out of my own way.