media won't play on plex server

I installed plex.  Was very easy using firecore - kudos.  However, I can not get the media to play.  It plays on the computer using PLEX just fine.  On the atv2 I can view all the movie choices that are on the computer, but when I select one it goes to the poster screen (full screen) but just sits there.  Never plays and never gives me any other options.  Am I doing something wrong? Anyone else ever experience this?