You may want to check the following link if you are using samba and the root of the drive have filenames with invalid Windows characters.http://wdtvforum.com/main/index.php?topic=3345.msg61146#msg61146
I always have had problems as I use my network drive with other unix-based systems and filesystems that, as Windows and ntfs, like to add invisible files in the root with invalid characters for thumgen and when TG go into them do not show anything. Even files created by Windows are read differently when the drive is plugged directly to the PC than when read via samba.
I have movie collections inside a folder an map that folder not the drive, ie
Instead of mapping "DriveName" I map the "Video" folder. (\\192.168.X.XX\DriveName\Video)
Hope this helps