Did you try connecting the source to the router with a wire? It worked for me even though my WDTV boxes were connected via wifi.
Also, what type of router are you using? It seems our issue isn't affecting everyone. Unfortunately, I don't think you always get honest answers here though. A lot of the posters here with a ton of posts actually work for WD. It's a conflict of interest for them to admit the device is flawed.
I am using a highend router...Netgear N900, but it doesn't make any difference. WIndows Shares on this device stinks bad all the way around.
Since we can really only use the device with a DLNA media server, we may as well return it in favor of the Sony that only costs 49 bucks (half the price). I have until January 24th to decide since I bought both of mine at Bestbuy. I could save a hundred bucks. Both brands work fine with a media server.