My Sony BDP-580S blu-ray play would see all the files on my N900 with USB drive but refused to play any of them. What ended up being the case for me was that while this router supports DLNA, it DOES NOT support DLNA conversion on the fly into a file format your other media devices can play. This caused me to re-convert all my movies and music into m4p and mp3 (non-lossless and has to be 192 bit or less encoding). This wasn’t an issue when I used my laptop as the DLNA server because win7 media center will auto convert files on the fly so I didn’t know this was a problem until using the USB ports on the router.
Because you said you are using a Sony TV, I would bet this is your problem as well with DLNA. If you check the super fine print and astricks/footnotes on your TV I would bet $1Mil that it says ONLY those 2 formats can be streamed to your Sony TV via DLNA servers. Since the router cannot re-encode on the fly, thus failed playback.