Changing DNS drops WDTV from home network

Hi folks

Have my WDTV LIVE streaming from my Readynas. Initially had it setup on network share and pointed the wdtv to individual folders on the nas. All good.

Then changed the DNS on the wdtv so i could use unblock us to access netflix. That worked fine and i watched a couple of shows. All good.

Then upon returning to the main menu on the wdtv its lost the shares and cant find the Nas. When i tell it to find the nas on the network it just sits hunting, trying to find the nas then gives up.

If i reset the wdtv and let it find the dns allocated by the router, all is fine again..

I thought the dns was for external lookup so why is it affecting my behind the router network?

Thanks for any advice

Ged