Last night, I got my first chance to try out VocalSync, but I must be doing something wrong, because I'm getting a loss of all sound from Sonar.
 
I have two vocal tracks.  They were initially two different takes of the lead vocal.  One track I edited with Melodyne, to turn into a Lead harmony track.  Basically deleting phrases and adjusting the pitch.  Afterwards, I bounced the edited track down.
 
Next I right clicked on the edited track and created a region effect with Vocalsync.  I chose the lead vocal track as the reference track.   After a few seconds, I got the two tracks and the Vocalsync editor knob.
 
Here's where the problem occurs.  As soon as I hit play to listen, the level meters for the harmony track goes off the scale and freezes, and the sound for everything disappears in Sonar.  I hit play, and hear nothing, from any of the tracks in the project.   If I cancel the Vocalsync edit, all the sound returns.
 
Any ideas?

I haven't tried it to tell you anything of use, but nobody has replied so:
 
Have you checked the videos on it?
https://www.youtube.com/watch?v=ao-wFsWI7qE
 

Thanks.   Yes, I watched that video before trying out vocalsync last night.  In the video, everything worked as advertised.   Unfortunately, It did not work that way for me.

I had essentially the same problem.
 
I still haven't solved. All I've established is that the problem happens with some projects and not others, and that Noel could not reproduce the problem when I sent him a file that was giving me trouble.

That's odd. Mine works fine. Are you running 64bit? Sounds like a similar problem I get with Channel Tool sometimes, and I suspect it's a 32-bit plugin issue inside my 64-bit environment (though I have no proof of that).
 
Just a tip, once you do have it working, it's still best to manually chop up the vocals and line them up as close to the original as possible, including a little time stretching if needed. Then bounce the clip and then only apply vocal sync as little as possible.  

Hi David,
 
I'd like to take a look at the project to see what is going on to cause the audio not to output. Would it be possible to send me the project to try to reproduce? You can PM me with a link (i.e. drop box or some other file sharing service). Please include the audio for the project. 
 
Thanks!

Didn't have a lot of time to experiment last night, but I made a little progress.  
 
Last night, I tried reversing the track selection, and vocalsync worked correctly.  Instead of creating a region effect on the harmony track and using the lead vocal as the guide,  I created the region effect on the lead vocal track, then selected the harmony track as the guide.  This worked.  Not sure why it froze when doing the opposite.
 

Oh the harmony singer must be better then.
VS was hearing the lead track and went ewww no way dude.
 
:-)