I read all the threads related to this issue and tried them all. I have Nero 7 installed and did uninstall the suggested pieces. I suspected since I have Extreme installed with Media Center that there might be a link.
Here is my solution:
In IE7 - Tools/Internet Options, Programs tab, Set Program Defaults button, Set Program Access and Computer Defaults, Custom, Choose a default media player:
Set it to Windows Media Player.
Hope this helps.
Microsoft Windows Vista