Silly me, with fun_plug not working you wouldn't be able to remote in and do a listing of Volume_1. Anyway do check if fun_plug permission is set to 777 (use Web File Server, right-click select Properties).
BTW, the content of fun_plug listed in your reply seem to be incomplete. Below is the correct one:
#!/bin/sh
# funplug for DNS-320 only !
#
# by Tamas v 1.3
# switch to safe working directory on ramdisk
cd /
# write a log, in case sth goes wrong
FFP_LOG=/mnt/HD/HD_a2/ffp.log
#FFP_LOG=/dev/null
exec >>$FFP_LOG 2>&1
# real path to ffp
FFP_PATH=/mnt/HD/HD_a2/ffp
# where to search for the install tarball
FFP_TARBALL=/mnt/HD/HD_a2/fun_plug.tgz
# setup script (used for ffp on USB disk)
FFP_SETUP_SCRIPT=/mnt/HD/HD_a2/.bootstrap/setup.sh
# rc file path
FFP_RC=/ffp/etc/rc
echo "**** fun_plug script for DNS-323 (2008-08-11 tp@fonz.de) ****"
date
# check for setup script. an example use for this is to load USB
# kernel modules and mount a USB storage device. The script is
# sourced, that means you can change variables, e.g. FFP_PATH to point
# to the USB device.
if [ -x $FFP_SETUP_SCRIPT ]; then
echo "* Running $FFP_SETUP_SCRIPT ..."
. $FFP_SETUP_SCRIPT
fi
# create /ffp link
echo "ln -snf $FFP_PATH /ffp"
ln -snf $FFP_PATH /ffp
# install tarball
if [ -r $FFP_TARBALL ]; then
echo "* Installing $FFP_TARBALL ..."
mkdir -p $FFP_PATH && tar xzf $FFP_TARBALL -C $FFP_PATH && /ffp/bin/tar xzf $FFP_TARBALL -C $FFP_PATH
if [ $? -eq 0 ]; then
echo "* OK"
fi
rm $FFP_TARBALL
fi
# suid busybox
if [ -x /ffp/bin/busybox ]; then
chown root.root /ffp/bin/busybox
chmod 0755 /ffp/bin/busybox
chmod u+s /ffp/bin/busybox
fi
# run fun_plug.init, if present
if [ -x /ffp/etc/fun_plug.init ]; then
echo "* Running /ffp/etc/fun_plug.init ..."
/ffp/etc/fun_plug.init
fi
# run fun_plug.local, if present
if [ -x /ffp/etc/fun_plug.local ]; then
echo "* Running /ffp/etc/fun_plug.local ..."
/ffp/etc/fun_plug.local
fi
# run commands
if [ -x $FFP_RC ]; then
echo "* Running $FFP_RC ..."
$FFP_RC
echo "* OK"
else
echo "$FFP_RC: Not found or not executable"
fi