Logon to SSH or console and complete the following (WINXP-12 is name of machine causing me greif)
~ # ps | grep WINXP-12
39770348 vmm0:WINXP-12
39790829 39799011 mks:WINXP-12 /bin/vmx
39790834 39799011 vcpu-0:WINXP-12 /bin/vmx
~ # kill -9 39790834