VirtualBox can't operate in VMX root mode. Please disable the KVM kernel extension, recompile your
type:
sudo modprobe -r kvm_intel
Run VirtualBox again that should fix the problem.
Transparent VirtualBox window with compiz manager
If you getting a transparent VirtualBox window, you can start VBox like this to fix the problem:
env XLIB_SKIP_ARGB_VISUALS=1 VirtualBox
references:
https://bugs.launchpad.net/ubuntu/+source/virtualbox-ose/+bug/292588
http://ubuntuforums.org/showthread.php?t=1160178
