Fix "Hyper-V cannot be installed: A hypervisor is already running" message in Fusion and Workstation

As you know, recent versions of VMware Workstation and VMware Fusion include the ability to run hypervisor-based applications inside a virtual machine running on those platforms.  However, even if you’ve configured your virtual machine to enable this support (using the instructions found in this article: VMware Fusion 5: Enable VT-x/EPT inside a virtual machine), when you attempt to install the Hyper-V component on Windows 8, you receive the error message “Hyper-V cannot be installed: A hypervisor is already running.”

This is easily correctable

1. First, shut down the Windows 8 virtual machine.
2. Make certain that you’ve enabled VT-x/EPT in your virtual machine (VMware Fusion 5: Enable VT-x/EPT inside a virtual machine)
3. Modify the vmx file associated with your Windows 8 virtual machine.  For my virtual machine, the vmx file is located at /Users/slowe/Documents/Virtual Machines.localized/Windows 8.vmwarevm/Windows 8.vmx.
4. Add the following lines to the end of the VMX file:
1. hypervisor.cpuid.v0 = “FALSE”
2. mce.enable = “TRUE”
5. Restart your virtual machine.

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