how to ACTUALLY set up a password protected network share

The trick is to actually NOT to use the File Access tab. I wish that tab wasn't there! (buried somewhere in advanced settings would be better).

1. Create a user.
2. Create a share.
3. Access the share settings.
4. Under Network Access / SMB:
   1. Uncheck Everyone.
   2. Check the relevant permission for your user.
5. Under File Access:
   1. Do NOT touch anything!
6. Done... That's it!

For convenience in Windows (Windows 10 can also be annoying with SMB credentials, so do that):

1. Search for Manage Network Passwords in Start Menu.
2. Add an entry with the path of your NAS and the user's credentials.
3. Use either the name or the IP of your NAS, but you'll have to use the same to connect. Or add an entry for each.

If you want to fix your existing share:

1. Access its settings.
2. Under File Access / Reset:
   1. Reset permissions.
3. Confirm the settings under Network Access.

(In most cases) There is NO need to use File Access as you already filter the users with the Network Access permissions.

Trust me, I have configured dozens of ReadyNAS units.