I have an external CAC card reader connected via USB. It was seen by Parallels and worked fine under Lion. Under Mountain Lion, Parallels simply doesn't see it.
I fixed my own problem. Knowing that Parallels requires kernel extensions at the lowest levels of the OS in order to function, I uninstalled Parallels (using the uninstaller), rebooted, reinstalled Parallels, then rebooted. Now everything is fine.
