If you are using Internet Explorer, this page should install the latest Microsoft XML Parser. If this does not work, then please go to Microsoft's web site and install it from there. You may need Microsoft Installer as well.
Note: Internet Explorer 6.0 may contain MSXML version 3.0, in which case there is no need to re-install it. However it may be advantageous to install Microsoft's XML SDK, as this contains documentation on methods that are used and exposed by the Schema Toolkit parser.