Indeed, I'm having the same problem. You say "some" videos don't work. May you link to one that does work, so I have something to watch before calling it a night? 
Many chess videos do not play
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Well, i corrected that to many just now as many videos do not work. Danny Rench's Panov attack was working sometime back.
I just saw your forum topic which you had already created for this problem.
http://www.chess.com/forum/view/community/chess-videos-quotvideo-stream-not-foundquot?lc=1#last_comment
Many of the videos are unable to play (it gives an error). All those seemed to be working yesterday. My flash player is working fine and I did watch one video just now.
Here is one of the video links:
http://www.chess.com/video/player/how-to-play-the-queens-gambit-ii
Can someone from staff pls check and update.