Old post but since I just bought a HP 477FNW Color Laser/scanner I had the same issues. Here is how I got it to work on Nas4free.
1. Make a new user called hpscan with a password and guest access
2. Make a folder called HP SCANS. Use the folder option to make sure its read write for all. (later you can restrict it) you just want to get it working for now.
3. On the NAS set up SMB settings then create a SMB share
4. In a web browser, type in ip of your HP printer/scanner.
ie. 10.0.0.62
The path should be the netbios name/smb share name
Do not use the actual path listed for the NAS server.
Use netbios name.
ie.
DON’T USE /mnt/ZPoolToshiba/HP SCANS
Use this ==>>>
\\DELL_NAS\HP Scans
This worked for me, Good Luck!
Another way to verify the path is to see if you can access that share from a windows machine. Don't map a network letter to it just use the windows 10 network view and it should list it. If you can browse to it with file manager then you can see the correct path but clicking in the file managers path line at the top.
Included are some of the configuration pictures.