Hi GoDeveloper,
We're working with Apple to investigate an issue where Mac OS X 10.8.x freezes (with 100% CPU usage) if it only has 1 processor core available and it starts running low on memory. It so happens that Mac OS will occasionally run a background process which will consume most of the guest RAM...
As dlhotka suggested, you'll need to add a second processor core to your VMs to avoid the problem for the time being. It's not a virtualization-specific issue: It's possible to artificially induce the same OS failure on a physical Mac, too...
Cheers,
--
Darius