Well Microsoft started pushing an update to Silverlight - updating it to version 2.0.40115.0 (40115? what are they thinking?) Of course it wouldn't install and there was no apparent way to uninstall the old version of silverlight. I tried even installing the new version right over the old but that failed also. So I dug around and tried some stuff.
Basically it involved downloading an old utilitiy from Microsoft that I had never discovered before. TheWindows Installer Cleanup Utility.
I installed it and it presented a list of apps to uninstall. I selected the old Microsoft Silverlight and it was gone. I ran Ccleaner (http://www.ccleaner.com) to clean up any registry stuff and then installed the new Silverlight 2 from Microsoft's site at http://silverlight.net/GetStarted/
That worked fine. btw I also saw a procedure to fix this problem which involved uninstalling Quicken. That seemed a little extreme to me.
This procedure is also nicely described at http://blog.computerplumber.ca/2008/11/error-with-microsoft-silverlight-...