Silverlight introduces three new file extensions (MIME types):
All these MIME types need to be configured in your IIS. By default, they are already implemented in IIS 7 (and above) in Windows Server 2008 and Windows Vista SP1.
If you run Windows Vista without SP1, you will have to add these extensions into your IIS.
1. Open IIS Manager.
2. Double-click MIME types in the IIS section.
3. Click Add....
4. Type the following information:
•File name extension: .xap
•MIME type: application/x-silverlight-app
5. Click OK.
6. Repeat for the other two types:
•File name extension: .xaml
•MIME type: application/xaml + xml
•File name extension: .xbap
•MIME type: application/x-ms-xbap
You have now configured your IIS to support Silverlight applications.