Have you installed the latest 4.2.6 and associated extension pack?
I've seen this a couple of times on older versions, there is a thread on the VB forums about it. In both cases following the thread and finding the vboxdrv.inf and selecting install cured it for me. This may or may not work if you're on 4.2.6.
For what its worth the thread is here https://forums.virtualbox.org/viewtopic.php?p=184903#p184903
It's possible the VB install is being hindered by your AV, might be worth disabling that just while you install VB.