Connect wdtv to nas

I am trying to use my nas as a media server i can view the video folder on my nas i have a mkv file in there. If I go to the wdtv and and connect to the nas as a media server i can see the video folder from the nas but then it will tell you there is no media present in the folder, I am using a synology 211 nas

Chances are the media server running on your Synology does not recognise MKV files, or does not understand that the WD TV Live can play MKV files.

Have you asked over in the Synology forums-

The Synology uPnP server recognizes mkv.

Are you connecting via uPnP? If so, are you using their default video folder? Are you running the DSM3.2 Beta which allows custom uPnP folders? Did you allow time for the Synology to index your files?

I have a DS-210j and Ds-411j with no issues using the network shares or uPnP.  How are you connected to the WDTV?