Adding VST Kills Audio

Running X1D in 64-bit with V-Studio 700.  Audio is via ASIO.
 
>> In at least one project, anytime I add another virtual instrument, all the audio becomes silent. <<  Sometimes the bass guitar goes off even without the addition of another VST.  I can usually fix that by restarting the audio engine.
 
There are already nine virtual instruments in the synth rack.  Sometimes I use fewer, sometimes many more, but nine is by no means unusual nor is it the limit.
 
If I add one more (e.g., Kontakt 5, EX Drummer, RealGuitar) all the audio goes off.  Restarting the audio engine does not fix it.  If I delete the VST insturment and restart the audio engine, the audio comes back.
 
Note that the audio only goes off for Sonar.  If I go to my desktop and play an mp3 or other sound source, i still hear the audio through the speakers connected to the V-Studio.
 
If it matters, this project was created in Sonar 2 a long time ago and most of the instruments have been replaced or redone.  This is by no means the only project I imported so I have no idea what is causing the pain with this one.
 
Here is what is in the synth rack:
RealGuitar 2
RealStrat
Acoustic Legends - Strumming (running in Kontakt 5 free player)
Ivory Grands (Steinway for comping)
SI-Bass
SessionDrummer 3
Ivory Grands (Yamaha for solo lines)
Acoustic Legends - Lead lines (Kontakt 5 free player)
EZ Drummer
 
Tested removing one ZVST (one of the Kontakt instances) and then adding another VST (EZ Drummer). In this case, the audio works.

Somehow, more than the nine virtual instruments cuts-off the audio.

Note that opening a second project also kills the audio.

Thanks for responding, CJ.  It is not really like a normal drop-out (at least as I have experienced them) and I don't get the Sonar drop-out msg.  All the audio just goes off and stays off.  Once I add that last VST, it is as though someone pulls the plug on audio.  If it played for a while and then dropped out, it would be easier to understand.

I will check the buffer, though.  Maybe there is something there. 

Do you think there is anything to my 32 v 64-bit VST idea?  Most of my Sonar problems are VST related.

Thanks.

I ran into something similar to this a while back.  My problem was actually caused by dropouts because my buffer value was set too low...but it would turn off the audio engine.  No sounds at all.  I had to click on the audio engine icon in the tool bar at the top and turn it back on.

Once I adjusted the buffer value to a higher value...the audio engine ran fine....but it caused latency.


Edited to add:

This is probably a different problem than what mine was....mine usually happened when I stopped playback...then I couldn't hear anything from the soft synths until I turned the audio engine back on.  Your problem actually sounds different than what I was experencing.

Thanks for responding, CJ. It is not really like a normal drop-out (at least as I have experienced them) and I don't get the Sonar drop-out msg. All the audio just goes off and stays off. Once I add that last VST, it is as though someone pulls the plug on audio. If it played for a while and then dropped out, it would be easier to understand.

I would try raising your ASIO buffer as i said in post #4.
A higher buffer may fix your issue. You wont know until you try it. Raise it in increments until the audio plays back