I am using the latest ATV Flash (v1.1.1), specifically having issues with Media Player streaming .dvdmedia documents.
For some reason, when trying to play a movie that I ripped using RipIt, which created the .dvdmedia document, I seem to be getting the error: unable to establish network connection.
If I play this movie from my MackBook Pro, it all works fine but will not play within Media Player.
Other movies that I have in this same shared directory with .avi extensions work.
Media Player is broken with a number of media types. Some files work, but many others fail miserably with a number of different error conditions. I and others have opened trouble cases and uploaded logs, and you should too. The more reports they get the more they will understand how lacking Media Player is at the current release level.
Hopefully the Firecore guys can get Media Player up to some level of reliability soon as it would be so much nicer to have a reliable top menu level media player instead of having to jump into XBMC to view almost everything.