Changes?
I installed two new Sonivox plugs. They played fine directly from the keyboard.
Then I ran Sonar and they seemed to auto install fine.
But now I have no sound.

Some projects the now time doesn't move and others it moves but no sound
At first my soundcard/controller (BR800) did not show up in audio devices but after rerunning sonar, are there now.
Outputs show up as BR800 ok in the consoles IN/OUTs
No mutes on. 
I can play youtube videos so the sound is ok
Ideas?

I have the same issue but with plugs installed during X1 or sooner... the sound just disappears with NO ERRORS but after about 2 or 3 minutes of hitting stop and play, it will start up again.

Very strange.... I wonder if this is tied into why UAD2 plugins aren't working at all in X2 for me and many others.  UA is aware of this issue and working on it but perhaps this is some inherent bug in X2?

Jim

I've had this as well. It turns out that somehow an input gain of the plug, or something like that, was the culprit. For guitars I would use the IK's white compressor and sometimes the gain knob would magicly turn itself down. It could have been an issue with the control surface I have though where I may have bumped it and that was enough.

In my case, I haven't even used the new plug in a project yet.
ALL projects are silent, not just projects with new plugs.

Then it sounds like a routing issue. Somewhere, something must be set wrong.

ASG had a similar problem, http://forum.cakewalk.com/tm.aspx?m=2337537
looks like it was a path issue.  if you've moved any folders, might want to msg him to see which folders he moved back.

I have not moved folders.
I uninstalled the sonivox stuff but no joy. 
I remember it telling me during install it was installing a program that I had to reboot before it took affect.
What's next? re-install Sonar?

I re-installed Producer and it plays!!   I did have the same "no play problem" but on a whim, changed Preferences/playback Timing master from none to BR800( my sound card/controller)