You need to add proper MIME types from the HELM control panel to enable SilverLight support for your website:

Below are the steps to add MIME types:

1) Login to the Helm control panel.
2) Select the domain name for which you wish to add MIME types.
3) Click on the MIME Types icon.
4) Enter xaml in the Extension dialog box and application/xaml+xml in the MIME type box.
5) Click the Save button.