This error message usually indicates that some kind of software-based
synthesizer ("SoftSynth") is being used.  A software synth works by taking
control of a sound card’s audio components to create a virtual synthesizer.  
In the process, it will not allow any other application to access the sound
card's audio.  Hence the ‘Wave Device Is Busy’ error.

To eliminate this error, disable the SoftSynth from within Digital
Orchestrator: 

1) Load a song that contains digital audio. 

2) Click Options -> MIDI Port Setup, and set all "MIDI Out" ports to "None".

3) On "MIDI Out" Port 1, test each available driver option by playing the
   song.  Do not assign the drivers that cause the error message to appear. 

4) Assign the driver(s) that appear to be functioning properly, to the 
   MIDI Out Ports.  This should eliminate the problem.