This isn't ideal, but as a work-around you could try converting each midi track to audio by going to the Tracks window and right clicking on a track. You can then select AUTO CONVERT INDIVIDUAL MIDI TRACK TO AUDIO TRACK. If it does this ok, you can do the same for the other tracks and then try merging the audio to a wave file. It would, at least, be useful to know if it will merge audio.

ROG.