Well, this is sort of quiet, but suffice it to say older version of Tivo Desktop are known not to play with SMB mounted file systems, aka the DNS321. The new version of Tivo Desktop Plus is 2.8 and there is a successful reg edit that makes it work for storing your Tivo Recordings on a DNS-321. It worked for me, so just passing it along.
Here's what worked ( posted by MattJ on the Tivo Community Forum)
http://www.tivocommunity.com/tivo-vb/showthread.php?s=97285ed18d8ba7230e1ba5230c5ff881&t=300764&page=31. Copy the "My Tivo Recordings" from the default location to its new home on the NAS. Make sure you include the desktop.ini in the copy. (As mentioned this is hidden by default)
2. Regedit and modify "LocalRootPath" under "HKEY_CURRENT_USER\Software\TiVo\Desktop\Modules\TivoNowPlay ing\Config". This should be set to point to the location of the "My Tivo Recordings" folder on the NAS.
3. start TiVo Desktop and transfer a program.
4. (optional for Desktop Plus) regedit and modify "OutputPath" under "HKEY_CURRENT_USER\Software\TiVo\Desktop\Converter" Change this to point to whatever location you want to use on the NAS.