Current Silverlight versions is Silverlight 5 (5.0.61118.0)?
FWIW I have tht installed. As an experiment I removed Silverlight.plugin from my Internet Plug-Ins and launched Safari and went to that page you referenced above. While I didn't get any errors reported the format of the page was different than when I had the Silverlight.plugin installed.
I am not aware of any preferences Silverlight creates. Other than the plugin the only other thing the installer installs is a folder in /Library/Microsoft/Silverlight. There is a text file in there with the version number. So perhaps that the problem, i.e., make sure you have the correct version of Silverlight. Or you could just try reinstalling Silverlight for the heck of it.
Remember if you do (re)run the installer, like any other thing that installs an internet plugin, be sure to restart your browser.