I don't know about the specifics of your drive, but I recently ran into a similar problem with my WD MyBook Live NAS: Apparently the latest release of iTunes conflicted with the drive's ability to act as an iTunes server.
Western Digital has announced that they are releasing a firmware update that will address this issue, but in the meantime the NAS simply serves as backup.
Best to contact the maker of your device for possible solutions and workarounds. Growing iTunes libraries are a big driver of sales in the NAS market, and manufacturers are aware of the issue.