I am trying to upgrade my Mac (Snow Leopard, Macbook Pro Core i7 2.66GHz, 8GB RAM) from ParallelsDesktop-parallels-en_US-6.0.11828.615184 to ParallelsDesktop-parallels-en_US-6.0.11992.625164. After the upgrade (no errors), when I launch a virtual machine, I get a dialog saying that I do not have virtualization turned on and another that says the Parallels drivers cannot be loaded. The output from "sudo kextstat | grep prl" is empty and the directory "/System/Library/Extensions/prl_*.kext" does NOT exist. It looks like the drivers were not installed. If I revert to the older version (11828.615184), everything works again. How do I fix this?