I am having a similar problem, possibly the same problem.
When i try to open a video in youtube the message comes up that i either have javascript turned off or an old version of Flash Player. i have downloaded the newest version of flash.
when i play videos on video.google.com they work fine and on other sites, but it just doesn't work on youtube.
apologies if this seems like a bread & butter problem but i haven't much of a clue about this and hope someone can help!