I did have Sonivox crashes with Windows 7 64bit. I Tried many things, adjusting the latency, etc. As strange as this is, I tried using Jbridge (Even though this is for running 32bit plugs in a 64bit environment), and this helped somewhat. But I still got the odd Sonivox crash.
I did not know about the pressing learn button - but I probably have done that with the projects I am using.
Now that I have upgraded to a fully patched Windows 10 64bit system, I no longer get crashes in any of Sonivox products. Their single instrument Taylor Guitar was really bad in Windows 7, but in Windows 10, no more crashes.
I have Sonar Platinum 2017.2 (The latest version as of 9 March 2017)
I am not sure what's different about my Windows 10 64bit system, but I have many Sonivox products (including Big Bang Cinematic Percussion v2.5) and do not have any of these crashing issue anymore. My round trip latency is 6ms.
I am currently in the middle of a project that uses Orchestral Companion - Brass, Orchestral Companion - strings and Big Bang Cinematic Percussion v2.5 and various other non Sonivox VST. I have not had this project crash.