While running VirtualBox on Mac OS X (especially on a netbook or notebook) you may find the following problem:
Your virtual machines do not start because VT-x is enabled and not supported. When you try to disable the VT-x you find that it is checked and greyed out so you can’t uncheck it.
Here is the solution for this problem: Edit the virtual machine XML file to disable VT-x and then lock the file. This way, Virtualbox will not be able to activate this option again.
To edit the file, go to your Mac OS X user folder -> Libraries -> VirtualBox -> Machines -> Machine Name folder and edit the XML file that exists there.
You will find a line:
<HardwareVirtEx enabled=”true” exclusive=”true”/>
Change this line to:
You are not done yet. You will also need to LOCK the file for editing, else Virtualbox will overwrite it again and reenable the VT-x option. To lock the file, right click on it, click Get Info and in the window that appears, enable the “Locked” option.
Now, run VirtualBox again and VT-x will remain disabled for this virtual machine.