In my experience if you connect to a esxi host directly you use the root account which is like the administrator on a windows machine.
do you know the root password of your host? can you try with that account?
if the permission denied is still there when you use the root account I'd say the issue is on your windows machine. I'd try to give "everyone" write access to that folder on your d: drive and try again.
I actually never used the vifg-user.pl command. Looking at the documentation (vSphere 6.0 Documentation Center ) it seems to be intended to manage users and not to test a login or determine the role of a user. But I could be mistaken of course