For what it's worth, you're not the only one. My HD1000S won't stream my content from my NAS. Admittedly it does list the videos when I browse the folders but most (the vast majority) won't play - it says 'cannot play this format' or similar.
All AVIs ripped in Handbrake. The weird bit is a couple of movies DO play fine but they were ripped in exactly the same way.
Can't be bothered to explore it at the moment as everything plays absolutely fine via my PS3 so just use that to stream instead.