VirtualBox VERR_ACCESS_DENIED
I think you may be hitting El Capitan's System Integrity Protection [SIP] which is preventing access..

Borrowed from How do I disable System Integrity Protection (SIP) AKA &quot;rootless&quot; on OS X 10.11, El Capitan? ...

Apple's documentation covers disabling SIP, About System Integrity Protection on your Mac.

An article on lifehacker.com lists these steps:


  
  Reboot your Mac into Recovery Mode by restarting your computer and holding down Command+R until the Apple logo appears on your screen.
  Click Utilities > Terminal.
  In the Terminal window, type in csrutil disable and press Enter.
  Restart your Mac.