For me the suggested fix of watching the video as the administrator then returning to a user account resolved my problem. I was attempting this with Firefox v4.0.1
One thought that occurs to me to add to the previous suggestion to log in as administrator.
Logging in as administrator is not the same as logging in using an account in the administrator group, or with administrator rights. It means logging in using the account "administrator".
A small distinction, and one I can't authoritatively define, but the difference exists. This is not the first time I have had software that you could install from an administrator account (or right click install as administrator) which would not work properly.
But when I actually logged in as the administrator it would.