How to fix "Droid4X Install failed!" absolutely works !
Today I've solution to solve this problem.
First: Check on your Launchpad if Droid4X installed you were found Droid4X icon in Launchpad.
Second: Try to launch Droid4X in Launchpad. if you get this message while launching Droid4X or anything.
If you already have VirtualBox then try to uninstall using AppCleaner or anything like that.
Fourth: If you uninstall finished then try to install latest VirtualBox that you've downloaded.
Fifth: Launch Droid4X in Launchpad.
Sixth: We've fixed it.