I am having this issue since I bought this player, right now I have 220.127.116.11 FW installed, but my luck didnt change.
All files that play, stutter after 30 / 50 Minutes, no matter the IQ, I suffered that with files of 800MB or with 4,5GB at 720p
I have the buffalo wireless adapter and a USRobotic (USR8054) G router.
The only way to solve this that I found (not always works) is rewind some seconds the movie and then hit play again, after that the stuttering gone.
Thanks a lot for your help!!!