How to (re)enable YouTube videos on Safari with Flash plugin 10.2? [duplicate]

Possible Duplicate:
The browser doesn't show videos on Youtube

Youtube videos appear as a black box only in safari 5.0.3, since flash payer has been updated to 10.2. They work if I change the User Agent to Safari 4.0.3 using the Developer menu, but this is not permanent.

Flash Player 10.1 is no longer downloadable, so I don't know how to downgrade. User agent setting are not permanent, or I don't know how to set them fixed.

Maybe, it is a bug in YouTube embedding, because Flash sites like that from Adobe work. I am relativly sure that the new flash plugin is the problem, because I have to macbooks with OS X 10.6.6 and Safari 5.0.3. The only difference if the version of the flash plugin: 10.1 shows youtube videos, 10.2 not.

I'm not sure the flash version is the reason. ALso the working mac has been installed with OS X 10.6 from scratch, the not working has been updated from an 10.5.

I had this problem while running ClickToFlash 1.6b9 (the original general browser plug-in, not the Safari 5.x extension). Even with ClickToFlash disabled via the checkbox in ClickToFlash's preferences, it still happened. I ended up dragging the ClickToFlash plug-in out of /Library/Internet Plug-Ins/ and restarting Safari, and it went away.