Hello everyone.
I also encountered problems playing my content, both files locally on my computer and from my 2TB FreeNAS NAS server. Got the error message "File format not supported". This of course frustrated me, as the DLNA support meant that in theory I could ditch my future HTPC project and save some money, and also saved me from yet another box in the living room.
The supplied software from Samsung was a utterly useless and was ditched in a flash. The media sharing in Windows Media Player 11 wasn't quite right, so I tried around a few other alternatives, one of them being TVersity. I liked it straight away, but was of course sad when I saw I couldn't play my files.
Being a one that never likes to give up without a fight, I did some testing and found that by setting the default profile (read: Media Playback Device) to "Playstation 3" under the general settings page, I was able to playback all my content without a glitch!
So I suggest you all to try the same and report back your findings. Worked fine for me, and I can't see a reason why it won't for you guys!
Good luck!

)