Please post hear the code that you use for insert the silverligh object into the html feature, so we can check if you have any error.
this is a example from my code
<div id="silverlightControlHost"><object width="500" height="280" type="application/x-silverlight-2" data="data:application/x-silverlight-2,">
<param value="black" name="background" />
<param value="/ClientBin/ImageFlow3D.xap" name="source" />
<param value="Path=/Services/GalleryDataService.ashx?pageid=18&mid=27,UseReflejo=true,TypeFile=jpg,ImageHeigth=160,ImageWidth=250" name="initParams" />
<p>This content requires Microsoft Silverlight.</p>
<p><a style="text-decoration: none;" href="http://go.microsoft.com/fwlink/?LinkId=149156"><img style="border-style: none;" src="http://go.microsoft.com/fwlink/?LinkId=108181" alt="Get Microsoft Silverlight" /></a></p>
</object></div>