Have a look at Brokenwire.NET’s article on the subject.

I’ll briefly mirror the instructions here:

  1. Open regedit.
  2. Search (Ctrl+F) for VirtualBox Host-Only Ethernet Adapter.  Keep searching until you’re inside HKLM\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318} — you’ll probably be highlighting the DriverDesc key.
  3. Add/modify a DWORD value, called NdisDeviceType, and give it a value of 1.
  4. Restart the machine.