Progress state: E_FAIL
VBoxManage.exe: error: Failed to create the host-only adapter
VBoxManage.exe: error: Code E_FAIL (0x80004005) - Unspecified error (extended info not available)
VBoxManage.exe: error: Context: "int __cdecl handleCreate(struct HandlerArg *,int,int *)" at line 66 of file VBoxManageHostonly.cpp
The only thing that worked for me is to download this fix (https://www.virtualbox.org/attachment/ticket/14040/VBox-Win10-fix-14040.exe), run it as administrator and vagrant up.
The box for the fix will appear, just leave it there and just type in vagrant up and everything should work, for me at least. After the VM is running, close it as per instruction from the virtualbox ticket.