- Shutdown Virtualbox completely.
- Start Terminal from the Applications/Utilities folder
- Copy and paste this command on a single line, where “Windows 8.1″ is replaced by the name you gave to the virtual machine you need to change:
vboxmanage setextradata "Windows 8.1" VBoxInternal/CPUM/CMPXCHG16B 1
- The command does not respond with a result, which actually means it is successful.
- Start Virtualbox and your virtual machine, and proceed to install Windows 8.1 as before.
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