I'd just like to emphasize that the offending process need not be on the DNS-323 - I had Memeo running on a desktop configured to backup to the DNS-323, and then reformatted the drives in the DNS-323 and not reconfigured Memeo, so Memeo would keep on searching for it's folders, which did not exist, and that would prevent the DNS_323 from going into standby.
The quick & easy way to determine if it is an internal or external process that is preventing the unit from going into standby is to disconnect the network cable and wait for the standby period to elapse, watch closely, because it is possible for it go into standby and then "wake up" immediately after.