virtualbox.org

I am running VirtualBox Version 4.3.28 r100309 on a Windows 8.1 Pro 64 bit host. My vm is Windows 7 Ultimate 64 bit.
When I attempted upgrade to Windows 10 on the vm, I received a compareexchange128 error.
Using an admin cmd, entered vboxmanage setextradata [7c] VBoxInternal/CPUM/CMPXCHG16B 1 .
Received this
VBoxManage.exe: error: Could not find a registered machine named '[7c]'
VBoxManage.exe: error: Details: code VBOX_E_OBJECT_NOT_FOUND (0x80bb0001), compo
nent VirtualBox, interface IVirtualBox, callee IUnknown
VBoxManage.exe: error: Context: "FindMachine(Bstr(a->argv[0]).raw(), machine.asO
utParam())" at line 803 of file VBoxManageMisc.cpp

Any assistance would be appreciated.
PS The vms path is in the windows environment setting.

You don't need the "setextradata" anymore.
Windows 10 won't run in a VM with a "Win7" OS setting. Change the VM type to "Windows 8.1 64bit" and try again.

what is the output of