Session drummer 2 muted in instrument window only

I can play sounds from Session Drummer but only if I click on the Sonar 8.3 project window. As soon as I click on the Session Drummer instrument window the sound is muted. The GUI responds to my mouse clicks and shows that I am auditioning drum pads, but there is no sound. Once I click on the Sonar project window again it will sound the drum. It's as if my sound card shuts off for the soft synth unless it plays through Sonar.
 
Any ideas on why the sound is muted in the instrument window?
 
Thanks, I appreciate it.