by the way here is a link to one of the threads on this:

http://answers.microsoft.com/en-us/windowslive/forum/skydrive-files/sorry-for-some-reason-we-cant-play-this-video/65d39178-ceec-4c8d-83ac-a4e43a32a4ba

there are several and all seem to be the same problem with playing back video.