A user has Flash Player 9 (or other version) installed on their system and everything works fine with IE6. That user then runs the IE7 update and their computer stops showing Flash content on sites like above or other Flash sites. However, if the user goes to some other sites with Flash content, the content will play just fine, even if the site requires the Flash 9 Player.
I’m not sure of the official cause for this, and am still doing some research into what causes it, but a first guess I have is that when you upgrade from IE7, the browser install is not correctly reinstalling your existing Flash Plugin, so scripts that check for the Flash Player are failing, but since the plugin file is there, if you visit a site that does not use a detection script (like SWFObject) you will see the Flash content just fine.
There may not be a solution to this for the sites using detection scripts - they rely on a series of Windows registry entries that seem to be missing after an IE7 upgrade.
For users, here is a fix that worked for me:
Quit all open programs. This step is important because other programs may be using the Flash Player, and if they are, the uninstaller will fail silently.
If you are still having problems after running the uninstaller and reinstalling the plugin, please post a comment with your system setup and other relevant details. (And remember, sometimes a system restart can make a difference with problems like this, so try that first).