Sunday, 1 December 2013

VirtualBox 4.3.4 VT-x error.

Hi, today when I start Windows in VirtualBox it display this error
Failed to open a session for the virtual machine W7.  VT-x is not available. (VERR_VMX_NO_VMX).  Result Code: NS_ERROR_FAILURE (0x80004005) Component: Console Interface: IConsole {8ab7c520-2442-4b66-8d74-4ff1e195d2b6}
I google this error and found this post on VirtualBox forum that solved the problem.
But the command on that post is not complete...
VBoxManage modifyvm vmname longmode off
So mine virtual machine is called "W7"...
VBoxManage modifyvm w7 longmode off
 In terminal...

"VBoxManage: error: Could not find a registered machine named 'w7'
VBoxManage: error: Details: code VBOX_E_OBJECT_NOT_FOUND (0x80bb0001), component VirtualBox, interface IVirtualBox, callee nsISupports
VBoxManage: error: Context: "FindMachine(Bstr(a->argv[0]).raw(), machine.asOutParam())" at line 455 of file VBoxManageModifyVM.cpp"

you can see this error is because of the lower case, again in terminal...

VBoxManage modifyvm W7 longmode off
"VBoxManage: error: Invalid parameter 'longmode'"

but if added -- at the beginning of longmode it will work and solve the problem.
VBoxManage modifyvm W7 --longmode off
I hope this help some one.


  1. Ran into the exact same problem and also found this forum post via Google. Had to apply the same corrections that you figured out, too. However, without that post I would've had no clue at all how to address this issue. Hats off to people sharing their knowledge like that person and you!

  2. Thanks I'm happy that this help you.