Hi nc,
Based on the article Add Silverlight to a page using the Silverlight Web Part, I would like you to note the following things:
1. The Silverlight Web Part acts as a host for the Silverlight application. Users must have the Silverlight plug-in installed on their computers to run Silverlight applications.
2. Locate the XAP File for the Silverlight applications that you want to publish. You must save this file to a network location that can be accessed from your site by using a URL, such as a library on your site.
3. Test the application to make sure that it runs correctly from the network location where you stored it. An XAP file can be configured by the developer to refer to external files. If this is the case, you must make sure these external files are also available from the network location where you stored the XAP file for the application to work.
4. Copy the URL for the network location where the XAP file is stored. You must reference this location when uploading the application to the Silverlight Web Part. You cannot browse to the location from the Web Part interface so that you should have the location reference easily available before you start.
Thanks,
Cherry Wang