A recent issue I ran into was a website that prompted the user to install Silverlight.
He already had it installed, and I ensured it was the latest version. The website worked fine when other users logged in. It did not work even after making the user a local administrator.
It had to be a profile setting.
Long story short, I found a blog that referenced but didn’t solve my problem, HOWEVER, deep in the comments was a suggestion to check this ActiveX setting in MSIE. If it’s enabled, then disable it and Silverlight should work.