I have the same issue after I was prompted yesterday to upgrade my Flash player. With the new version, 2/3 of Flash pages do not work. But 1/3 do work !
Example of page that does not work with new version of Flash :
http://www.youtube.com/ (the whole site)
http://www.adobe.com/fr/products/flashplayer/ (Adobe's official Flash page !)
Example of page that does work with new version of Flash :
Here is my current configuration (the version test at http://kb2.adobe.com/cps/155/tn_15507.html works well) :
Player Version : WIN 10.0.22.87
Debug Player : no
Operating System : Vista
Browser : Internet Explorer 8
Locale : French
O.K. I got it to work. I downloaded the Adobe Flash uninstaller from http://kb2.adobe.com/cps/141/tn_14157.html I closed Internet Explorer and uninstalled Flash. Then I opened Internet Explorer and reinstalled Flash through the official Adobe Flash page. Now everything is working.
Anyway, the problem is solved now.
As the previous poster suggests, download the FP uninstaller from http://www.adobe.com/go/tn_14157
Also download the offline ActiveX installer for Internet Explorer: http://fpdownload.macromedia.com/get/flashplayer/current/install_flash_player_ax.exe
Close all browser windows, then run the uninstaller, followed by the installer.