Flash

I am trying to embed youtube’s link in my post with Flash. I enter the link and I see Flash icon when I am editing. However, when I publish the post, I see only white field. And if I click on, it says “Movie not loaded”. What could be the problem and what should I do?

P.S. In one draft the video appeared and then it disappeared when I tried to publish. Now, when I go back to the very same draft, there is no video.