What do you make of this, I found it in the online help.
Using a DXi synth will simplify the problem, since the MIDI and audio tracks are routed to the same audio device in this case.
(Mainly this portion, I have Vista 64 bit)
Note: The VSC-DXi is not compatible with 64-bit operating system - an alternative is to use the ForteDXi or TTS-1 soft synth. If you aren't using a DXi synth, find out whether it's MIDI or Audio/RealTracks that you aren't hearing, or both.