The D-Link DNS-320 needs a different store-passwd.sh than the one supplied with Fonz fun_plug. Basically it is very simple if you look at the contents:
#!/ffp/bin/sh echo "Saving Userdata to /usr/local/config/" cp -f /etc/passwd /usr/local/config/ cp -f /etc/group /usr/local/config/ cp -f /etc/shadow /usr/local/config/ cp -f /etc/samba/smbpasswd /usr/local/config/
Run the following command to download it to the NAS:
wget http://wolf-u.li/u/172/ -O /ffp/sbin/store-passwd.sh
Then proceed with the installation of Fonz fun_plug.