Are the folders that you want to stream in your Public Folders? Do you need to enable Media Service on the Public Share.
I found this comment buried deep in comments on another forum that may help.
" I had assumed that enabling the NAS as a Media Server was sufficient and by so doing it automatically selected the media in the Public Share. It was a reasonable assumption because the Our Music, Our Pictures, and Our Videos folders were located there by default. That may have in fact been the case in earlier firmware versions, but now it is also necessary to designate which Share is the Media Service Share. That's accomplished by editing the Share's features. Simple!!
As soon as I enable Media Service on the Public Share, all of the media files were found and displayed in WMP, on my AV receiver and on my BD player. The music files in albums are sorted alphabetically vs. order on the album, but I can live with that. Now I'm finally getting the service from my NAS that I had intended."
Is the firmware for your NAS up to date?