We are talking about a drive attached to Volumio Primo and trying to get access over the network, correct?
Networking is a bit tricky on Windows, but if you can see it and its contents, it may be an access issue on the drive, not the network.
I noticed that if I formatted my usb drive with xFat, it would not allow access, although I could see the drive. When I then formatted as NTFS, I was able to get guest access which allowed me to read and write.
So, that is why I think it is a permission issue. For the life of me I cannot see anywhere in the Volumio settings where it addresses Volumio user permissions.