Play / pause button not responding

I’m using the djay Pro for Windows software in combination with a Hercules mp3 LE controller. During my last dj session the play pause button did not respond anymore. Neither via the controller, nor via mouse-click on the screen. It worked perfectly in the beginning. It worked again after I closed the app and restarted it. However, after a couple of minutes the same problem occured again on one desk. I could drag and drop a song to the desk, but I couldn’t stop the track. Any recommendation?